The polynomials $x^2 - 7x + b = 0$ and $x^2 + 2x - 2b = 0$ have a root in common.  Enter all the possible values of this root, separated by commas.
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<|im_start|>user
The polynomials $x^2 - 7x + b = 0$ and $x^2 + 2x - 2b = 0$ have a root in common.  Enter all the possible values of this root, separated by commas.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
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user
0,4
The polynomials $x^2 - 7x + b = 0$ and $x^2 + 2x - 2b = 0$ have a root in common.  Enter all the possible values of this root, separated by commas.
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