解方程组：I.x+2y-z=6 2x+y+z=9 3x+4y+z=18 II.x-y=3 x²-y²=18

题目

解方程组：I.x+2y-z=6 2x+y+z=9 3x+4y+z=18 II.x-y=3 x²-y²=18

答案

1 x=3,y=2,前面两式相加得x+y=5,后面两式相减得,x+3y=9,.
2,分解后面方程式得x+y=6,算出x=9/2,Y=3/2