All but B, as on B an a can be factored out
This question is asking "Where does cosine equal

?"
Based on our unit circle values and the domain of the cos^{-1} function, we see that at 30 degrees, or

, cosine is equal to

.
60%. That is the probability.
1.
√(16+20)=√36=6
C
2.
√(21-9)=√(12)=(√4)(√3)=2√3
B
3. 2*√3=2*1.73205=3.464
B
1.C
2.B
3.B