已知m²-mn=2,mn-n²=5,则3m²+2mn-5n²=?
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已知m²-mn=2,mn-n²=5,则3m²+2mn-5n²=?
已知m²-mn=2,mn-n²=5,则3m²+2mn-5n²=?
已知m²-mn=2,mn-n²=5,则3m²+2mn-5n²=?
3m²+2mn-5n²
=3(m²-mn)+5(mn-n²)
=3x2+5x5=31