What is the exact value of -sec(3pi/4)

I keep getting -2/√2, but the answer is √ 2....
this is what I did:
3pi/4 = 135 degrees
cos(45 + 90)
cosAcosB - sinAsinB
(√2 /2 * 0 - √2 * 1) = -√2 / 2
then flip it and * by -1 because of -sec
= 2/√2

That's correct ...2/√2 = √2. All you need to do is just rationalize the denominator (multiply top and bottom by √2) to get √2.

Hope that helps!