早教吧作业答案频道 -->数学-->
已知x3+y3-z3=96,xyz=4,x2+y2+z2-xy+xz+yz=12,则x+y-z=()A.6B.7C.8D.9
题目详情
已知x3+y3-z3=96,xyz=4,x2+y2+z2-xy+xz+yz=12,则x+y-z=( )
A.6
B.7
C.8
D.9
A.6
B.7
C.8
D.9
▼优质解答
答案和解析
x3+y3-z3+3xyz,
=[(x+y)3-3x2y-3xy2]-z3+3xyz,
=[(x+y)3-z3]-(3x2y+3xy2-3xyz),
=(x+y-z)[(x+y)2+(x+y)z+z2]-3xy(x+y-z),
=(x+y-z)(x2+2xy+y2+xz+yz+z2-3xy),
=(x+y-z)(x2+y2+z2-xy+xz+yz),
∵x3+y3-z3=96,xyz=4,x2+y2+z2-xy+xz+yz=12,
∴96+3×4=12(x+y-z),
解得x+y-z=9.
故选D.
=[(x+y)3-3x2y-3xy2]-z3+3xyz,
=[(x+y)3-z3]-(3x2y+3xy2-3xyz),
=(x+y-z)[(x+y)2+(x+y)z+z2]-3xy(x+y-z),
=(x+y-z)(x2+2xy+y2+xz+yz+z2-3xy),
=(x+y-z)(x2+y2+z2-xy+xz+yz),
∵x3+y3-z3=96,xyz=4,x2+y2+z2-xy+xz+yz=12,
∴96+3×4=12(x+y-z),
解得x+y-z=9.
故选D.
看了已知x3+y3-z3=96,x...的网友还看了以下:
在解方程组{ax+by=26 cx+y=6 的时候小冲求得正确得解为x=-4 y=-2,但小牛把c 2020-05-13 …
1、(2x+3)^2-25=02、(x+7)^2=3x(x+7)3、4(x-2)^2=x^2-44 2020-06-10 …
已知f(x)是实数集R上的减函数,且f(x/y)=f(x)-f(一),f(2)=1,解不等式:f( 2020-06-27 …
Java的几道运算题,越快越好写出下列表达式的值,设x=3,y=7,yn=true.(1)x+y* 2020-07-17 …
解方程3-5x+72=-x+174,去分母正确的是()A.12-2(5x+7)=-(x+17)B. 2020-07-18 …
解方程.x÷5.5=21.22x-0.5×3=0.426x-2.7=1.238.94+5x=33. 2020-07-19 …
解方程.x÷5.5=21.22x-0.5×3=0.426x-2.7=1.238.94+5x=33. 2020-07-19 …
quadndg求多重积分的计算速度问题我有一个求9重积分问题,积分区间从一个数积到无穷,函数具体形 2020-07-23 …
已知x,y,z满足x+1/y=3,y+1/z=1,z+1/x=7/3,则xyz的值为多少?x+1/y 2020-10-31 …
(7017•福州质检)(1)计算:|-1|+178+(-3.1人)0-(17)-1.(7)先化简,再 2020-11-12 …