Question

докажите тождество:
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Answer 1

$\frac{(m+n)^{2}- (m-n)^{2} }{2} = \frac{ m^{2}+2mn+ n^{2}- m^{2}+2mn- n^{2} }{2} = \frac{4mn}{2} = 2mn$

2mn=2mn