such functions are known as restricted functions..
here sin-1x and cos-1x are res. funcs as have restrcted domains from -1 to 1
thus, -1 < x < 1
now, f(x) = sin-1x2 + cos-1x3 + tan-1x4
= (6sin-1x + 4cos-1x + 3tan-1x)/12 = (2sin-1x + 3tan-1x + 2pi)/12
now, on diff. we can easily find the min val. and max val. of the expression...