4(-2mn+2m+3n)-2(3m+5n-mn),其中m+n=3,mn=-1

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4(-2mn+2m+3n)-2(3m+5n-mn),其中m+n=3,mn=-1

4(-2mn+2m+3n)-2(3m+5n-mn),其中m+n=3,mn=-1
4(-2mn+2m+3n)-2(3m+5n-mn),其中m+n=3,mn=-1

4(-2mn+2m+3n)-2(3m+5n-mn),其中m+n=3,mn=-1
4(-2mn+2m+3n)-2(3m+5n-mn)
=-8mn+8m+12n-6m-10n+2mn
=-6mn+2m+2n
=-6mn+2(m+n)
=-6*(-1)+2*3
=6+6
=12

你好,砖前级:

4(-2mn+2m+3n)-2(3m+5n-mn)
=-8mn+8m+12n-6m-10n+2mn
=2m+2n-6mn
=2(m+n)-6mn
∴当m+n=3,mn=-1时,
原式=2×3-6×(-1)=6+6=12

4(-2mn+2m+3n)-2(3m+5n-mn)
=-8mn+8m+12n-6m-10n+2mn
=-6mn+2m+2n
=-6mn+2(m+n)
=-6×(-1)+2×3
=12

4(-2mn+2m+3n)-2(3m+5n-mn)
=-8mn+8m+12n-6m-10n+2mn
=-6mn+2m+2n
=-6(-1)+2(m+n)
=6+6=12