已知x=m²-2mn+n²,y=m²-2mn-n².当m=1,n=2时,求x-[y-2x-(x-y)]的值
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![已知x=m²-2mn+n²,y=m²-2mn-n².当m=1,n=2时,求x-[y-2x-(x-y)]的值](/uploads/image/z/7216110-54-0.jpg?t=%E5%B7%B2%E7%9F%A5x%3Dm%26%23178%3B-2mn%2Bn%26%23178%3B%2Cy%3Dm%26%23178%3B-2mn-n%26%23178%3B.%E5%BD%93m%3D1%2Cn%3D2%E6%97%B6%2C%E6%B1%82x-%5By-2x-%28x-y%29%5D%E7%9A%84%E5%80%BC)
已知x=m²-2mn+n²,y=m²-2mn-n².当m=1,n=2时,求x-[y-2x-(x-y)]的值
已知x=m²-2mn+n²,y=m²-2mn-n².当m=1,n=2时,求x-[y-2x-(x-y)]的值
已知x=m²-2mn+n²,y=m²-2mn-n².当m=1,n=2时,求x-[y-2x-(x-y)]的值
x-[y-2x-(x-y)]
=x-y+2x+x-y
=4x-2y
=4(m²-2mn+n²)-2(m²-2mn-n²)
=4m²-8mn+4n²-2m²+4mn+2n²
=2m²-4mn+6n²
=2-8+24
=18
x-[y-2x-(x-y)]
=x-y+2x+x-y
=4x-2y
=4(m²-2mn+n²)-2(m²-2mn-n²)
=2m²-4mn+6n²
=2×1²-4×1×2+6×2²
=2-8+24
=18