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Here is the question: sec(θ-150 degrees)=4

(solving for theta is greater than or equal to -180, but less than or equal to 180)

So I know that sec is the reciprocal of cos so I changed the equation to cos(θ-150)=1/4

from there I did the inverse of cos to get θ-150 = 75.52, then I added 150 to get θ= 225.5

I then drew a cos graph and from this would assume that the answers are 134.5 and -134.5...... but the answer booklet for my textbook says they are -134.5 and 74.5!!

This is probably so simple but I have no clue what I'm doing wrong!!!