Find the exact values of sec(x)=7.

I know that cos(x)=1/7.
I know that sin(x)= sqrt(1-91/4900).
I know that tan(x)=1.

I know how to do the problem but I'm not really sure why, and I'd like to know. I got 4sqrt(3).

Please help!

so, cos(x) = 1/7 and x is in QI or QIV

so, x = 81.79 or 278.21 degrees

no idea where you came up with your values for sin(x) and tan(x). ??