Question

How do you evaluate sec(150)?

Answer 1

`sec150=1/cos150=1/(cos(180-30))=-1/cos30=-1/(1/2)=-2`

Explanation:

The only difficulty would be in `cos(180-30)=-cos30`. This is easy to see if we remember the formula `cos(180-30)=cos180cos30+sen180sen30=-1·1/2+0·sqrt2/2=-cos30=-1/2`

Answer 2

`-(2sqrt3)/3`

Explanation:

`sec150=1/(cos150)`

now

now

`cos150=-cos(180-150)`

`cos30=sqrt3/2`

`:.sec150=1/(-sqrt(3)/2)`

`=-2/sqrt3=-(2sqrt3)/3`