已知m²+n²=5,试求代数式(5+2m²+3n²-mn)-(4m²+5n²-mn)的值
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![已知m²+n²=5,试求代数式(5+2m²+3n²-mn)-(4m²+5n²-mn)的值](/uploads/image/z/657855-63-5.jpg?t=%E5%B7%B2%E7%9F%A5m%26%23178%3B%2Bn%26%23178%3B%3D5%2C%E8%AF%95%E6%B1%82%E4%BB%A3%E6%95%B0%E5%BC%8F%285%2B2m%26%23178%3B%2B3n%26%23178%3B-mn%29-%EF%BC%884m%26%23178%3B%2B5n%26%23178%3B-mn%EF%BC%89%E7%9A%84%E5%80%BC)
已知m²+n²=5,试求代数式(5+2m²+3n²-mn)-(4m²+5n²-mn)的值
已知m²+n²=5,试求代数式(5+2m²+3n²-mn)-(4m²+5n²-mn)的值
已知m²+n²=5,试求代数式(5+2m²+3n²-mn)-(4m²+5n²-mn)的值
原式=5+2m²+3n²-mn-4m²-5n²+mn
=-2m²-2n²+5
=-2(m²+n²)+5
=-10+5
=-5
(5+2m²+3n²-mn)-(4m²+5n²-mn)
=5+2m²+3n²-mn-4m²-5n²+mn
=5-2m²-2n²
=5-2(m²+n²)
=5-10
=-5