计算:(2m-3)(2m+3)+(3n-m)(m+n)

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计算:(2m-3)(2m+3)+(3n-m)(m+n)
计算:(2m-3)(2m+3)+(3n-m)(m+n)

计算:(2m-3)(2m+3)+(3n-m)(m+n)
原式=(4m²-9)+(2mn-m²+3n²)
=3m²+2mn+3n²-9
(2mn-m²+3n²)是把(3n-m)(m+n)里面的分别相乘
=3mn-m²+3n²-mn
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3m2+2mn+3n2-9

3m²-3n²-2mn-9

原式=(4m²-9)+(2mn-m²+3n²)
=3m²+2mn+3n²-9

如图