1.3a(6a+3)(6a-3),当a=-2/3时.2.化简求值:[(2x-y)^2-(3x+y)(3x-y)+5x(x-y)]÷(-y),其中x=1/9,y=-3
问题描述：
1.3a(6a+3)(6a-3),当a=-2/3时.
2.化简求值:
[(2x-y)^2-(3x+y)(3x-y)+5x(x-y)]÷(-y),其中x=1/9,y=-3
答
1.原式=3a（36a^2-9)=3*(-2/3)(36*4/9-9)=-2*7=-14
2.原式=(4x^2-4xy+y^2-9x^2+y^2+5x^2-5xy)/(-y)=
(-9xy+2y^2)/(-y)=9x-2y=1+6=7
答
解一:3a(6a+3)(6a-3),当a=-2/3时.代入得:3*(-2/3)*[6*(-2/3)+3]*[6*(-2/3)-3]=-2*(-1)*(-7)=-14解二:[(2x-y)^2-(3x+y)(3x-y)+5x(x-y)]÷(-y)=[(4x^2-4xy+y^2)-(9x^2-y^2)+5x^2-5xy)]÷(-y)=[4x^2-9x^2+5x^2+y^2+y^2-...