已知m^2-mn=21,mn-n^2=-12,求代数式m^2于n^2与m^2-2mn+n^2的值

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已知m^2-mn=21,mn-n^2=-12,求代数式m^2于n^2与m^2-2mn+n^2的值
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已知m^2-mn=21,mn-n^2=-12,求代数式m^2于n^2与m^2-2mn+n^2的值
已知m^2-mn=21,mn-n^2=-12,求代数式m^2于n^2与m^2-2mn+n^2的值

已知m^2-mn=21,mn-n^2=-12,求代数式m^2于n^2与m^2-2mn+n^2的值
m^2-n^2=21-12=9
m^2-2mn+n^2=21-(-12)=33

m^2-mn=21 1
mn-n^2=-12 2
1+2得
m^2-mn+mn-n^2=m^2-n^=21-12=9
1-2得
m^2-mn-(mn-n^2)=m^2-2mn+n^2=21-(-12)=33

m^2-n^2=21-12=9
m^2-2mn+n^2=21-(-12)=33