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`y = cos ^(-1)((1 - x^(2))/(1+ x^(2))) 0 lt x lt 1`

Answer» `y = cos ^(-1)((1 - x^(2))/(1+ x^(2)))`
Let `x tan theta` ltbgt `rArr theta = tan^(-1) x `
`rArr y = cos^(-1)((1 - tan^(2)theta)/(1 +tan^(2)theta))`
`=cos^(-1)((cos^(2)theta-sin^(2)theta)/(cos^(2)theta + sin^(2) theta))`
`= cos ^(-1)(cos2theta)= 2theta= 2tan^(-1)x`
`rArr (dy)/(dx) = 2 (d)/(dx) tan^(-1)x = (2)/(1+ x^(2))`.


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