Saturday, December 31, 2011
integral of (cos x)^3
the (cosx)^3 is split into (cos²x )cosx
the cos²x is written as 1 - sin²x (using trigonometry formulae)
then the substitution t = sinx , dt=cosx dx is used
more explanation is given below
click here for integration formulae
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Tuesday, December 27, 2011
integral of cosx / [ 1- cos²x]
∫ { cosx / [ 1- cos²x] } dx = ∫ { cosx / [sin²x] } dx
= ∫ {1 / sin x} {cos x / sin x} dx
= ∫ cosec x cot x dx
= - cosec x + c
click here for integration formulae
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Wednesday, December 21, 2011
solving a quadratic equation by completing the square
solving a quadratic equation by completing the square
solve 2x² -4x -7 = 0
the equation can be written as 2x² -4x =7
dividing by 2 ( coefficient of x² )
x² - 2 x = (7/2)
note that coefficient of x is -2, take half of it that is -1,
square that and add the square to both sides,
use that to complete the square on the LHS x² - 2 x + 1² = (7/2) + 1²
(x-1)² = (9/2)
take square root x -1 = ± ( 3 / √2 )
x = 1 ± ( 3 / √2 )
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Tuesday, December 20, 2011
question on normal distribution
z = (x - 75) / 8 is the standard normal variate
we have to find k so that
P[X > k ] = 0.25
P[ z > (k-75)/8 ] = 0.25
refer standard normal tables (note that probability is given)
(k-75)/8 = 0.675 (approximately)
k = 80.4 marks approximately
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Thursday, December 8, 2011
buying tax saver elss mutual funds
So the concept of income tax breaks for investments in elss mutual funds seems to be still good for this financial year.
I recently bought some units of hdfc tax saver and sbi magnum tax gain mutual funds.
I went to the cams outlet at pattom and gave a copy of the kyc acknowledgement along with the cheque and application form as it was a new folio for the hdfc mutual fund.
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Saturday, December 3, 2011
buying a sewing machine
My wife wanted to buy a manually operated singer sewing machine. The shop keeper told us that some of the internal parts of that particular sewing machine could be easily accessed by the lay user. The singer sewing machine cost around Rs.5800 /-. We used an autorickshaw to take it from the shop. The sewing machine came with some spare bobbins, screw drivers, some lubrication oil, washers etc.
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