- #1

Liger20

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Hey, I have a problem that I worked out in a trigonometry book. I got different answers from what the book gave, but I think that I am right and the book is wrong. Could someone please tell me who is right?

## Homework Equations

Okay, they gave me the following problem: solve for x in secx^2-4=0 when 0 is less than or equal to x, which is less than or equal to 360.

Here is how the book solves it:

(secx-2)(secx+2)

secx-2=0 secx+2=0

secx=2 secx=-2

x=sec^-1(2) x=sec^-1(-2)

= 30, 330 = 150, 210

Okay, here's where I have a big problem: secant is the reciprocal function of cosine, right?

So if we evaluate x=sec^-1(2), we get cos^-1(1/2), which does not equal 30 and 330 when plugged into the calculator. Same situation with x=sec^-1(-2).

I am pretty sure that this is a horrible typo, but I would be delighted to be corrected otherwise.