1.

Find the maximum and minimum values of `(sin^(-1)x)^3+(cos^(-1)x)^3,`where `-1lt=xlt=1.`

Answer» `(sin^-1 x)^3 + (cos^-1 x)^3 = (sin^-1 x + cos^-1 x)^3 - 3sin^-1 x cos^-1 x (sin^-1x + cos^-1 x)`
`y = (pi/2)^3 - 3sin^-1 x (pi/2 - sin^-1 x )*(pi/2)`
`y= pi^3/8 - 3pi^2/4 sin^-1 x + 3 pi/2 (sin^-1 x)^2`
`3 pi/2 theta^2 - 3 pi^2/4 theta + pi^3/8 -y=0 `
`(theta - pi/4)^2 - pi^2/16 + pi^2/12 -2y/(3y) = 0`
`(theta- pi/4)^2 + pi^2/48 - (2y)/(3 pi) = 0`
`-pi/2 <= sin^-1 x <= pi/2`
`-(3pi)/4 <= sin^-1 x - pi/4 <= pi/4`
`0 <= (sin^-1 x - pi/4)^2 <= (9pi^2)/(16)`
`pi^2/48 <= 24/(3 pi) <= (9pi^2)/16 + pi^2/48`
`y max= (7pi^2)/8 ; y min = pi^3/32`
Answer


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