3x^2-x=1求6x^3+7x^2-5x+1990.
1个回答
6x^3+7x^2-5x+1990
=6x^3-2x^2+9x^2-3x-2x+1990
=2x(x^2-1)+3(x^2-1)-2x+1990
=2x*1+3*1-2x+1990
=1993
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解下列方程:(1)-4x+6=5x-3(2)1-3x=7x+4(3)-2x-7x+5=3x-x-6(4)-3x+3=1-