先化简再求值:(x-1)(x+2)+(2x-1)(x+5)-3(x的平方-6x-1),其中x=7/2抱歉,还有几题2(x-y)^2-(y-x)^2-(x+y)(y-x); x=3,y=-2;(3/4a^4b^7+1/2a^3b^8-1/9a^2b^6)/(-1/3ab)^2; a=1/2,b=-4;[(-2xy^2)^2x^3-2x^2(2xy^2)^3*1/2y]/4x^4y^2 x=1/2,y=-1;

问题描述:

先化简再求值:(x-1)(x+2)+(2x-1)(x+5)-3(x的平方-6x-1),其中x=7/2
抱歉,还有几题
2(x-y)^2-(y-x)^2-(x+y)(y-x); x=3,y=-2;
(3/4a^4b^7+1/2a^3b^8-1/9a^2b^6)/(-1/3ab)^2; a=1/2,b=-4;
[(-2xy^2)^2x^3-2x^2(2xy^2)^3*1/2y]/4x^4y^2 x=1/2,y=-1;

(x-1)(x+2)+(2x-1)(x+5)-3(x的平方-6x-1)
=x的平方+2x-x-2+2x的平方+10x-x-5-3x的平方+18x+3
=28x-4
=28*7/2-4
=94

(x-1)(x+2)+(2x-1)(x+5)-3(x的平方-6x-1)
=x平方+x-2+2x平方+9x-5-3x平方+18x+3
=28x-4
=4(7x-1)
x=7/2 28x=14*7=98
所以28x-4=98-4=94