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=().](/uploads/image/z/594321-33-1.jpg?t=%E5%B7%B2%E7%9F%A5m%26%23178%3B-mn%3D2%2Cmn-n%26%23178%3B%3D5%2C%E5%88%993m%26%23178%3B%2B2mn-5n%26%23178%3B%3D%28%29.)
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=().
m²-mn=2 (1)
mn-n²=5 (2)
(1)×3+(2)×5
3m²-3mn+5mn-5n²=2×3+5×5
3m²+2mn-5n²=31