Isn't the value of pi/2 radians "0", though? I bet that's why she's facepalming. His math is wrong!
Now if it was her cosine.
Actually sine of pi/2 is 1.
pi/2 cosine is 0.
Oh yeah. I haven't had to use trigonometry in a while, and I was too lazy to look it up. Now that you mention it, I remember.