Question

How do you solve and find the value of `cos^-1(sin^-1 90)`?

Answer 1

One cannot evaluate `cos^-1(sin^-1 90)`, because `90` is outside the domain for the inverse sine function:

`theta = sin^-1(x); -1 <= x <= 1`

Also, please observe that the inverse sine function returns an angle with the units of either degrees or radians; this is incompatible with the argument of the inverse cosine function, which requires a unitless quantity.