1,x(y-x)－y(z-x)+z(x-y)
=xy-x^2-yz+xy+xz-yz
=2xy-x^2-2yz+xz
这道题是不是错了
是不是
x(y-z)－y(z-x)+z(x-y)?
=xy-xz-yz+xy+xz-yz
=2xy-2yz
2,(-2/3*10^3)^2(1.5*10^4)^2
=(-2/3)^2*10^6*1.5^2*10^8
=(-2/3*1.5)^2*10^(6+8)
=1*10^14
所以有15位
3,体积是(3x-4)*2x*x
=6x^3-8x^2
4,(x+m)(x+0.2)
=x^2+(0.2+m)x+0.2m
不含x项
0.2+m=0
m=-0.2
5,中间的一个为n
则另两个是n-2和n+2
它们的积是n(n-2)(n+2)=n(n^2-4)=n^3-4n
6,三角形的面积是(2x+6y)(4x-5y)/2
=2(x+3y)(4x-5y)/2
=(x+3y)(4x-5y)
=4x^2-5xy+12xy-15y^2
=4x^2+7xy-15y^2
7,(5x^3y)(－4xyz)(－5xyz)
=[5*(-4)*(-5)]*(x^3*x*x)(y*y*y)(z*z)
=100x^5y^3z^2
8,(3x^2y－2xy^2－4xy)(－4x^2y^2)
=3x^2y*(－4x^2y^2)－2xy^2*(－4x^2y^2)－4xy*(－4x^2y^2)
=-12x^4y^3+8x^3y^4+16x^3y^3
9,(a+1)(a^2－2a－3)+(a－1)(a^2－2)－(2a^2－1)(a+1)
=a^3-2a^2-3a+a^2-2a-3+a^3-2a-a^2+2-2a^3-2a^2-a-1
=-4a^2-8a-2
=-4*1-8*(-1)-2
=-4+8-2
=2
10,(x+3)(x-2)+(x－1)(x+3)－2(x^2－x+8)
=x^2+x-6+x^2+2x-3-2x^2+2x-16
=5x-25
=5*5-25
=0