Question

What is `cos [Sec ^-1 (-5)]`?

Answer 1

#cos(arcsec(-5)) = -1/5

Explanation:

Knowing that `cos(x) = 1/sec(x)` we can say that

`cos(arcsec(-5)) = 1/sec(arcsec(-5))`

Since `sec(arcsec(x)) = x` we have

`cos(arcsec(-5)) = 1/(-5) = -1/5`