(x-2y)2+(x+2y)(x-2y)-(x-3y)(x-y)计算结果是什么?x等于-4,y等于0.5代入后是多少

显示全部楼层 · 2011-3-10 23:03:23

第一个括号后的2是平方的意思!!!谢!!!

千问 · 2011-3-10 23:03:23

(x-2y)^2+(x+2y) (x-2y)-(x-3y) (x-y)= (x-2y) [ (x-2y) + (x+2y) ] - (x-3y) (x-y)=(x-2y)2x - (x-3y) (x-y)= 2x^2 - 4xy - x^2 +4xy - 3y^2= x^2 - 3y^2代入后 = (-4)^2 - 3 * 0.5^2 = 16 - 3/4 = 15 1/4 =15.25

千问 · 2011-3-10 23:03:23

结果是x^2-3y^2带入后为12.25

千问 · 2011-3-10 23:03:23

2x-8y+4xy-3y^2-20.75