find arc sec 251 help me understand how to solve this thank

find arc sec -2.51.

help me understand how to solve this, thank you.

Solution

let us say

x = arc sec(-2.51)

sec x = -2.51

but sec x = 1/cos x

so 1/cos x = -2.51

cosx = -1/2.51

cos x = -0.398

x = arc cos-0.398

now using calculator

x= 113.5 degree