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已知|m+6|+(m+2n)²=0,求(4m²-2mn-5n²)-(5m²-6mn+2n²)的值...
已知|m+6|+(m+2n)²=0,求(4m²-2mn-5n²)-(5m²-6mn+2n²)的值
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因为|m+6|>=0 (m+2n)²>=0
所以要使|m+6|+(m+2n)²=0 只能 m=-6 n=3
代入得:(4m²-2mn-5n²)-(5m²-6mn+2n²)
=-m²+4mn-7n²
=-171
所以要使|m+6|+(m+2n)²=0 只能 m=-6 n=3
代入得:(4m²-2mn-5n²)-(5m²-6mn+2n²)
=-m²+4mn-7n²
=-171
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