Given that $\cos a = \frac{1}{3}$ and $\cos b = \frac{1}{4},$ compute $\cos (a + b) \cos (a - b).$
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Given that $\cos a = \frac{1}{3}$ and $\cos b = \frac{1}{4},$ compute $\cos (a + b) \cos (a - b).$
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
-\frac{119}{144}
Given that $\cos a = \frac{1}{3}$ and $\cos b = \frac{1}{4},$ compute $\cos (a + b) \cos (a - b).$
train