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