## Wednesday, December 31, 2008

### revision of some math topics for class XII (12th) ISC , CBSE

answer: (pi/4) - (1/2) more explanation on this area question

evaluate integral of (x ² +3x) with limits 1 to 3 using summation (limit of a sum)

answer: (62/3) explanation of integration by limit of sum question

evaluate integral of [ x*exp(x)] / (x+1) ² dx

answer: exp(x) / (x+1) + C explanation on integration by parts of exp(x)[f(x) + f '(x)] form

∫ { [log x] / x² } dx log x refers to lnx

answer: -(1+ln x ) /x +C explanation on integration by parts for ∫ { [log x] / x² } dx

∫ dx / [ (x-2) (1 + x²)]

answer:(1/5)ln(x-2) -(1/10)ln(1 + x²) -(2/5)arctan(x)+C explanation on integration by partial fraction

problem on matrices

answer: (x= -1) explanation of matrix problem

problem on determinant

explanation of determinant problem

solve x+y = 2 ; 2y-z = 0 ; -x-y+z = -1 using cramer's rule (using determinants)

answer : x = 3/2 , y =1/2 , z=1 explanation on solution of equations using cramer's rule

solve 3x+4y = 17 , -4x+3y =44 using matrix inversion

answer: x = -5; y =8 explanation on solving system of equations using matrix inversion

solve cos ² x (dy/dx) + y = tanx

answer : y = tanx - 1 + C exp(-tanx) explanation

ntegral of ln(sin x) from 0 to pi/2

answer: (pi/2)ln(1/2) for explanation: integral of ln(sin x) from 0 to pi/2

.∫ (x²) sin x dx

answer: -x² cosx +2xsinx+2cosx+C ;explanation: integration by parts

if y= tanֿ¹ { √ [(1-x)/(1+x)] } find dy/dx

answer: -1 / sqrt (1-x²) ;explanation:diff. by trig. substitution

show that the semivertical angle of a right circular cone

of maximum volume and given slant height is tan ֿ¹(√2 )

explanation of maxima / minima problem

show that the height of a closed cylinder of given volume and minimum surface area

is equal to its diameter explanation of minimising surface area

There is a figure (norman window) in which a rectangle is surmounted by a semicircle with diameter along one side of the rectangle .If the perimeter is given find the radius of the semicircle if the area is to be maximum (maximum amount of light is to be admitted into the room) explanation

find the equation of the tangent at t = pi/3 on the curve x=2cost , y = 3sint

answer: 3x + 2ysqrt(3) =12 explanation of finding equation of tangent

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## Tuesday, December 30, 2008

### some resources on weight loss

distinguish between hunger and emotional feelings like anxiety, boredom etc

chew your food slowly

drink sufficient quantities of water

increase physical activities

avoid stress

cut down on usage of butter

snack on fruits instead of candy

use steamed food instead of fried

cut down on cookies

cut down on carbonated beverages

use fresh fruits instead of canned fruits with syrup or juice

cut down on ice cream

avoid high fructose corn syrup (HFCS) this will get rid of most of the junk food

use more fish in your diet

use lean meat

try not to skip breakfast

cut down on chips

avoid fast food

use foods rich in fibre (avoid refined food)

use vegetables

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## Monday, December 29, 2008

### south africa win cricket series 2-0 against australia

http://news.bbc.co.uk/sport2/shared/fds/hi/statistics/cricket/scorecards/2008/12/15095/html/scorecard.stm

http://content-ind.cricinfo.com/ausvrsa2008_09/engine/current/match/351682.html

This is australia's first home test series loss in nearly 16 years.

In this match australia seemed to be carrying some players who had injuries and some who were out of form.

The fall of aussie cricket team seems to have started at the beginning of the year when they lost the perth test against india (even though australia won that series 2-1) . Perth was the last place anyone expected india to beat the australians . In the CB one day series also , India easily defeated the aussies 2-0 in the best of three finals.

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### beware of student education loans

Most of the students might be taking on these loans in the hope of landing jobs with high wages as soon as they graduate. But they have to remember that many things can happen in the duration of a 4 to 5 year course. If for some reason, the student has some arrear papers by the time he finishes the course, or if the job market for that particular branch of study is not very strong , the student will find it very hard to find a job to support himself and pay off the student loan (some loans might have a 1 year or so grace period after the course duration before repayment starts. ). Even an average student will only start at an entry level position in his job ladder and will take many years before he might have enough experience to get the high wages that he might have dreamt of as a student.

So before you take out huge loans, read and do research about the interest rates(fixed/floating etc) , repayment details, relative chance of jobs in fields related to current education, aptitude of the student in the chosen field of study etc

## Sunday, December 28, 2008

### integral using cauchy's integral formula

pole is given by (2z-5)=0

z = 5/2 which lies inside the given circle

take the 2 common from the denominator to make it (z-a) form

take f(z)=cosz which is analytic inside and on the given contour

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## Friday, December 26, 2008

### disposable email

Most internet users must have seen that some internet sites ask you for your email addresses for registering. After that you will get tons of unwanted spam mail in your inbox and you spend a lot of time to delete them. Spam filters can help a little bit.There is another approach. There are some sites which provide you with alternate disposable temporary email addresses. You can give these temporary addresses when registering. Some of these services will forward the mail to your proper email address. Some of the services have no password so that anyone who knows your id can read your spam mail at the site. Some of the services delete all mail after a certain number of messages/amount of time. Some of the addresses are valid only for a certain periond of ime. Some services require some registration procedure while some allow direct usage.Before using such services please read their terms of services

### website counters

**website counters**

If you have a website you may like to see the number of people who visit your site, where your visitors come from, which pages are the most popular, which browsers and operating systems your visitors use and so on.

Sometimes your web-host themselves may provide you with some of these statistics. If you are using services like geocities they already provide you with some of these statistics.

Otherwise you will have to rely on counter solutions available on the internet or make your own counter.

Most of the counters available on the internet give you a piece of code which you copy and paste into your webpage. Most of the sites providing these counters will ask for your email address when you sign up. Some of the free counters may send small ads along with the counter.

Some examples of third party counters are

webstat.com (this counter is used extensively on my site They provide a free version for upto 20000 pageviews per month, and also a premium version/trial version )

statcounter.com(offers free edition for sites with upto 250000 pageloads per month and paid versions also if number of pageloads is higher)

Many more counters are available and can easily be located via search engines by searching for 'free page counters' or some similar search words.

Another approach to counters are php scripts.(first check if you can use php). There are many php scripts available on the net. Most of these require you to change your webpage from html extension to php extension. There may also be another small php file which contains the counter code to which you will link to from inside your webpage. Usually there may also be a text file to hold the count and optional image files to display the digits 0 to 9. (Also remember that the php code can be mangled by the auto correction features of webpage creating software like frontpage. Therefore it is better to enter the php code using a text editor after you have finished making your webpage). The php files are usually uploaded as ascii files.

some examples are

More counters based on php are available on the internet and can be located by searching for 'php counters' search engines.

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## Wednesday, December 24, 2008

### indian parliament passing bills without debates

The number of sittings per year of parliament also seems to be decreasing.

## Tuesday, December 23, 2008

### integral of [sin(lnx) ]/ x ² using substitution

use the substitution lnx= u or x = e^u

then use the std. formula for integral of {e^(ax)} sinbx given here

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change

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If x+18y+c=0 is a normal to y = 5x ² -12x + 1 , find the value of c

let x+18y+c=0 be a normal at (h,k) on the curve y = 5x ² -12x + 1

implies k = 5h ² - 12h+ 1 -------------(1)

y = 5x ² -12x + 1

diff. w.r.t.x dy/dx = 10x-12

slope of normal at (h,k) = -1 / (dy/dx) = -1 / (10h-12)

also slope of the given line x+18y+c=0 is -1/18

therefore -1 / (10h-12) = -1/18

solving 10h-12 = 18 or h =3

using equation(1) k = 5*3 ² - 12*3+ 1 = 10

therefore h=3 , k=10

x+18y+c=0 is a normal at (3,10) and should be satisfied by (3,10)

3 + 18*10 +c =0

c= -183

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## Sunday, December 21, 2008

### integration with adustment instead of long division/partial fractions

first we have to do long division since degree of numerator = degree of denominator

then we have to proceed to partial fraction

but in this method those have been replaced by adjusting the numerator in terms of the

denominator and then dividing term by term

integration formulae

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## Friday, December 19, 2008

### trigonometry problem

start from the LHS, introduce the conjugate

simplify the denominator using identity then divide term by term

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trigonometry formulae

for some other examples

prove that (cotA+cosecA-1)/(cotA-cosecA+1)=cosecA+cotA -----> (problem on trigonometry )

Prove that (tanxsinx) / (tanx+sinx) = (tanx-sinx) / (tanx sinx) -----> (problem on trigonometry )

find exact value of tan[22½ °] or tan (pi / 8 ) -----> (problem on trigonometry )

find exact value of tan15° without using calculator --------value of tan15° without using calculator

conditional identity : If A+B+C=Ï€,

prove that: sinA+sinB+sinC = cot(A/2).cot(B/2) [sinA+sinB-sinC] -----> (problem on conditional identity (trigonometry) )

graphs of trigonometric functions-----> (graphs of trigonometric functions )

prove that

{ tan((Ï€/4)+x) - tan((Ï€/4)-x)} / { tan((Ï€/4)+x) + tan((Ï€/4)-x) } = sin2x ---------trigonometry problem

prove that (cos²x - sin²x) / (cos²x + sinxcosx) = 1 - tanx -------------trigonometry problem

show that

tan(x)/[1-cot(x)] + cot(x)/[1-tan(x)]= 1+sec(x)csc(x) , x≠ n Ï€ /4 ---------trigonometry

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## Tuesday, December 16, 2008

### solving a quadratic equation by graphing

graph y = x² -2x -8 using a calculator or a piece of paper

the graph is shown below

see where the graph cuts the x-axis

in this problem x = -2 and x=4 are the roots

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### index of problems

### Integration formulae

Online guide to certain topics on integration for isc, cbse , plus two etcPAGE 1 BASIC INTEGRATION

PAGE 2 INTEGRATION BY SUBSTITUTIONPAGE 3 INTEGRATION BY COMPLETION OF SQUARES

PAGE 4 INTEGRATION BY PARTS

PAGE 5 INTEGRATION BY MANIPULATION OF NUMERATOR IN TERMS OF DENOMINATOR

PAGE 6 INTEGRATION USING PARTIAL FRACTIONS

PAGE 7 INTEGRATION OF 1 / [ACOSX +BSINX +C]

### integral of 1 / [9 + 7 cos² x]

### integral of x^3 / sqrt(9 - x^2) using substitution

### integral of tan ² x secx using substitution

### integral of ln(x) using integration by parts

### evaluate ∫ [1 / {x lnx}]dx

integral of e^(2x) / sqrt [1 + e^(2x)]integral of ∫ { lnx / [x^4]} dx

### integral of [sin(lnx) ]/ x ² using substitution

integration using partial fraction### problem on integration using trigonometry formulae integral of sin(5x)sin(8x)

### integral of arc(cosx) using integration by parts

if sqrt(x) + sqrt(y) = 1 find y" second derivative with implicit differentiation

equation of tangent to y =x^4 at the point where x=2

equation of tangent at (0,4) on x(y^3)+y+7(x^4) = 4

### solving a quadratic equation by graphing

### trigonometric identities

if (A-B) = pi/4 show that (1+tanA)(1+tanB) = 2tanAtrigonometry problem : show that 1/(1-cosx) =(cscx+cotx)cscx

trigonometry problem :show that [( tanx -sinx ) / (2tanx) ] = sin² (x/2)

finding sin( arctan(2) )

exact vaue of sin(arctan(4/3)-arccos(12/13))

exact values of certain trigonometric ratio

### problem on changing the base of a log

Complex

### integral using cauchy's integral formula

### real and imaginary parts of ln(x+iy)

### show that e^(ix) = cosx +i sinx using power series

### problem on sequences If Sn is the sum of the cubes of the first n natural numbers, find the sum of 1 / sqrt(Sn) where n varies from 1 to 2000

find the sum of all even natural numbers between 2 and 200 (both inclusive ) excluding the multiples of 3sum of n terms of a geometric progression 1 + 2 + 4 + 8 + 16 + ...

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to construct truth tables for [~ (p ^ q ) ]v (~r)

proof of boundedness law a+1 = 1 and idempotent law a+a=a in a boolean algebra

boundedness law in a boolean algebra

idempotent law in a boolean algebra

If G is an abelian group ,

let f : G -->G be defined by f(x) = xֿ¹ show that f is an automorphism on G problem on automorphism on abelian group

If G is a group and f :G -->G is defined as f(x) = a ֿ¹ x a for x in G and a is a fixed element of G

then show that f is an isomorphism of G onto G problem on automorphism in a group

analytical geometry

### centre and radius of a circle

correlation and regression

### derivation of regression line of y on x

### limits for the correlation coefficient

### changing recurring decimal to fraction

### derivation of mean and variance of binomial distribution

derivation of mode of the binomial distribution### approximation of an integral using binomial series

### mclaurin's power series for ln(1+x)

How many 10 paise and 25 paise coins does the man have in his purse? solution

X can do a piece of work in 2 hours, while Y can do the same piece of work in 4 hours.What is the time taken if X and Y do the work together? solution

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### problem on changing the base of a log

use the definition of log

refer note on properties of logarithms

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## Friday, December 5, 2008

### integral of tan ² x secx using substitution

regroup as tanx (secxtanx)

change tanx to sqrt(sec ² x -1)

use the substitution u = secx ; du =secxtanxdx

see below for more stepssome other examples

evaluate integral of { e^(1 /x^2)} / {x^3} -------------(integration by substitution)

evaluate the integral of [e^(-x) +1] ^2 ------------- integration after expansion using identity

integral of e^{x^(1/3)}-------------- e^{x^(1/3)}

integral of x / (x+1)^2-------------integration by adjustment

integrate 1/ (x^7 - x) -----------integration by adjusting

integral of ( ( 4 - x^2 )^( 3/2) ) with limits 0 to 1--------------integration by substitution

integral of [cosx (1+sin²x)] with 0 to Ï€ /6 as limits-------------integration by substitution

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## Thursday, December 4, 2008

### cbse model question paper for 2009

there are answers/ marking scheme also as far as the the math question paper for 12th is concerned

the questions were available on their website(contains flash i guess) cbse wesite

or in particular http://cbse.nic.in/curric~1/sample2009.htm

or http://cbse.nic.in/curric~1/sample.htm

a collection of some questions for a quick revision in some topics for 12th students (CBSE, ISC etc) is available here

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### verifying eulers theorem for homogeneous functions ?

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