Question

已知方程组{4x-3y-6z=0 x+2y-7z=0 且z≠0,则（x+y+3z）÷（4x-y-5z）=?结果和思路!

Answer 1

亲,题目看似很麻烦,仔细想还是有思路的.
解:由4x-3y-6z=0,(1式)
x+2y-7z=0(2式)
(2式)*4得:
4x+8y-28z=0(3式)
(3式)-(1式)得:
4x+8y-28z-(4x-3y-6z)=0
4x+8y-28z-4x+3y+6z=0
11y-22z=0
y=2z(4式)
将y=2z代入(2式)中得
x+2y-7z=x+2*2z-7z=x-3z=0
x=3z(5式)
将(4式)、(5式)代入
(x+y+3z)/(4x-y-5z)
=(3z+2z+3z)/(12z-2z-5z)
=8z/5z
=8/5