-7-9x=2x*-7求X值2.((x+y)/4)-((x-y)/3)=1((x+y)/4)+((x-y)/2)=93.(3/(x+1))-(4/(y-2))=2(1/(x+1))+(y/(y+2))=5第二第三题求XY两值

Question

-7-9x=2x*-7 求X值
2.((x+y)/4)-((x-y)/3)=1 ((x+y)/4)+((x-y)/2)=9
3.(3/(x+1))-(4/(y-2))=2 (1/(x+1))+(y/(y+2))=5
第二第三题求XY两值

Answer 1

-7-9x=2x-7

-9x-2x=7-7

-11x=0
x=0


2.((x+y)/4)-((x-y)/3)=1 ((x+y)/4)+((x-y)/2)=9
{3(x+y)-4(x-y)=12         1)
{(x+y)+2(x-y)=36          2)
1)+2)×2得：
x+y=84/5                      3)
2)×3-1)得：
x-y=48/5                       4)
3)+4)得：
x=66/5
3)-4)得：
y=18/5
{x=66/5,y=18/5


3.(3/(x+1))-(4/(y-2))=2  (1/(x+1))+(1/(y+2))=5
令1/(x+1)=a,1/(y+2)=b
{3a-4b=2                  1)
{a+b=5                     2)
1)+2)×4得：
a=22/7                      3)
2)×3-1)得：
b=13/7                      4)
{1/(x+1)=22/7,1/(y+2)=13/7
{x=-15/22,y=-17/13