Laws of cosine help (attaching pic)

Here's what I did:
2^2=3^2+4^2-2(3)(4)cos(theta)
4=9+16-24cos(theta)
4=25-24cos(theta)
-21=-24cos(theta)
.875=cos(theta)
arccos(.875)=28.96 degrees

Question

Laws of cosine help (attaching pic)

Here's what I did:
2^2=3^2+4^2-2(3)(4)cos(theta)
4=9+16-24cos(theta)
4=25-24cos(theta)
-21=-24cos(theta)
.875=cos(theta)
arccos(.875)=28.96 degrees   <- doesn't match any of the options

What am I doing wrong??
The options are 21, -21, 24,-24

anonymous · Answer

you need to find the value of 2*3*4*cos theta..., you dont need to find the value of theta

anonymous · Answer

Oh wow am I dumb....thanks!!

anonymous · Answer

you just need to read the question more carefully :)

directrix · Answer

2^2 - 3^2 - 4^2 = - 2(3)(4) cos(theta)
-21 = - 2(3)(4) cos(theta)
 21 = 2(3)(4) cos(theta)