Factor the following expression: $7x^2-63$.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Factor the following expression: $7x^2-63$.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
7(x+3) (x-3)
Factor the following expression: $7x^2-63$.
train