已知m^2-m=15 mn-n^2=-6 求3m^2-mn-2n^2=?

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已知m^2-m=15 mn-n^2=-6 求3m^2-mn-2n^2=?
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已知m^2-m=15 mn-n^2=-6 求3m^2-mn-2n^2=?
已知m^2-m=15 mn-n^2=-6 求3m^2-mn-2n^2=?

已知m^2-m=15 mn-n^2=-6 求3m^2-mn-2n^2=?
题目是m^2-m=15;
mn-n^2=-6 ;求3m^2-mn-2n^2=?
若是,答案如下:
3m^2-mn-2n^2
=3m^2-3mn+2mn-2n^2
=3(m^2-m)+2(mn-n^2)
=3*15-2*(-6)
=45+12
=57