_________-3(x^2-2b)=2x^2-b
问题描述：
_________-3(x^2-2b)=2x^2-b
m^4-2m^2n^2-2m^2+2n^2+n^4=m^4-2m^2n^2-()+n^4
多项式5x^2y-15x^2y^2与12xy^2+23x^2y^2-x^2的差是——
若ab=-2,a-b=1/4,则（ab-4a）+a-3b的值为
答
（1）__5x²-7b___-3(x^2-2b)=2x^2-b2x^2-b+3(x^2-2b)=2x²-b+3x²-6b=5x²-7b（2）m^4-2m^2n^2-2m^2+2n^2+n^4=m^4-2m^2n^2-( 2m²-2n² )+n^4（3）多项式5x^2y-15x^2y^2与12xy^2+23x^2y^2-...