Saturday, July 6, 2013

What is the function y if dy/dx=square root(1-x^2)/x^2?

We'll have to integrate dy to get the primitive funtion
Y.


dy =
sqrt(1-x^2)dx/x^2


We'll integrate both
sides:


`int` dy = `int`
sqrt(1-x^2)dx/x^2


Let x = sin t => dx = cos t
dt


t = arcsin x


`int`
sqrt(1-x^2)dx/x^2 = `int` sqrt[1-(sin t)^2]*cos t dt/(sin
t)^2


We'll apply Pythagorean identity to
numerator:


`int` [sqrt (cos t)^2]*cos t dt/(sin t)^2 =
`int` (cos t)^2dt/(sin t)^2


`int` (cos t)^2dt/(sin t)^2 =
`int` [1-(sin t)^2]dt/(sin t)^2


`int` [1-(sin t)^2]dt/(sin
t)^2 =`int` ` ` dt/(sin t)^2 - `int` dt


`int` [1-(sin
t)^2]dt/(sin t)^2 = -cot t - t + C


`int` sqrt(1-x^2)dx/x^2
= - cot (arcsin x) - arcsin x + C


The
requested primitive function Y is: Y = - cot (arcsin x) - arcsin x +
C.

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