化简求值:9x²-6xy+y²分之3x²-xy其中x=2分之1,y=-3分之2

问题描述:

化简求值:9x²-6xy+y²分之3x²-xy其中x=2分之1,y=-3分之2

原式

=x(3x-y)/(3x-y)²

=x/(3x-y)

=(1/2)/[3*(1/2)-(-2/3)]

=(1/2)/(3/2+2/3)

=(1/2)/(13/6)

=1/2x6/13

=3/13  (13分之3)