数学题,在线等,急,回答了给QB计算题（写过程）(x+2)(x+3)-(x+6)(x-1)(3a+1)(2a-3)-(6a-5)(a-4)(2a的2次方-3a-1)(a+2)-(a+1)(a+2)3(x-2)(x+1)-2(x-5)(x-3)化简求值(x-y)(x-2y)-(2y-x)(x-3y)-2(x-3y)*(x-4y),其中x=4,y=1.5已知一个梯形

Question

数学题,在线等,急,回答了给QB
计算题（写过程）
(x+2)(x+3)-(x+6)(x-1)
(3a+1)(2a-3)-(6a-5)(a-4)
(2a的2次方-3a-1)(a+2)-(a+1)(a+2)
3(x-2)(x+1)-2(x-5)(x-3)
化简求值
(x-y)(x-2y)-(2y-x)(x-3y)-2(x-3y)*(x-4y),其中x=4,y=1.5
已知一个梯形,上底长为a,下底长为b,高为h,若上底减少为原来的一半,下底增加到原来的2倍,高增加3倍,梯形面积会增加多少?
先化简,再求值
3z[a的2次方-3x(a-3x)]+a[9x的2次方-(3ax+a的2次方)]其中x=-1/3,a=-1/2
回答了的密语我,我会给你QB

Answer 1

注：x^2 就是x的二次方.a^3就是a的三次方.
1 (x+2)(x+3)-(x+6)(x-1)
=(x^2 ＋3x+2x+6)-(x^2 -x+6x-6)
=x^2 ＋3x+2x+6-x^2 +x-6x+6
=12
2,(3a+1)(2a-3)-(6a-5)(a-4)
=(6a^2 -9a+2a-3)-(6a^2-24a-5a+20)
=(6a^2-7a-3)-(6a^2-29a+20)
=6a^2-7a-3-6a^2+29a-20
=22a-17
3,(2a^2-3a-1)(a+2)-(a+1)(a+2)
=(2a^3+4a^2-3a^2-6a-2)-(a^2+2a+a+2)
=(2a^3+a^2-6a-2)-(a^2+3a+2)
=2a^3+a^2-6a-2-a^2-3a-2
=2a^3-9a-4
4,3(x-2)(x+1)-2(x-5)(x-3)
=(3x-6)(x+1)-(2x-10)(x-3)
=(3x^2+3x-6x-6)-(2x^2-6x-10x+30)
=(3x^2+3x-6)-(2x^2-16x+30)
=3x^2+3x-6-2x^2+16x-30
=x^2+19x-36
化简求值
(x-y)(x-2y)-(2y-x)(x-3y)-2(x-3y)*(x-4y),其中x=4,y=1.5
答：
(x-y)(x-2y)-(2y-x)(x-3y)-2(x-3y)*(x-4y)
＝(x^2-2xy-xy+2y^2)-(2xy-6y^2-x^2+3xy)-(2x^2-8xy-6xy+24y^2)
=32y^2-12xy
=32*1.5^2-12*4*1.5
=32*1.25-48*1.5
=40-72
=-28