In triangle $ABC$, $\angle ABC = 90^\circ$, and point $D$ lies on segment $BC$ such that $AD$ is an angle bisector.  If $AB = 105$ and $BD = 42$, then find $AC$.
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You are a helpful assistant.<|im_end|>
<|im_start|>user
In triangle $ABC$, $\angle ABC = 90^\circ$, and point $D$ lies on segment $BC$ such that $AD$ is an angle bisector.  If $AB = 105$ and $BD = 42$, then find $AC$.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
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In triangle $ABC$, $\angle ABC = 90^\circ$, and point $D$ lies on segment $BC$ such that $AD$ is an angle bisector.  If $AB = 105$ and $BD = 42$, then find $AC$.
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