Question

sistema a. x+y=6. y=2x. b. x+y=11. x-y=5. c.2x-5y=8. x-2y=3. d.x+y=7. x-y=5. e 5x+2y=9. x+2y=5

Answer 1

y = 2x       x + y = 6
                 x + 2x = 6
                 3x = 6  
                   x = 6/3
                   x = 2

y = 2x
y = 2.2
y = 4                           S = {( 2 , 4 )}

---------------------------------------------------------------------------------
 
 x + y = 11
 x  - y =   5
--------------------
 2x     = 16
  x = 16/2
  x = 8

x + y = 11
8 + y = 11
y = 11 - 8
y = 3                 S = {( 8 , 3 )}

---------------------------------------------------------------

  2x - 5y = 8
    x - 2y = 3  .(-2)

  2x -  5y =   8
- 2x + 4y = - 6
-------------------
        - y = 2 .(-1)
          y = - 2 

x - 2y = 3
x - 2. (-2) = 3
x + 4 = 3
x = 3 - 4
x = - 1            S = {( - 1 , - 2 )}

---------------------------------------------------------------------------

x + y = 7
x -  y = 5
-------------
2x    = 12
x = 12/2
x = 6

x + y = 7
6 + y = 7
y = 7 - 6
y = 1          S = {( 6 , 1 )}

------------------------------------------------------------

 5x + 2y = 9
   x + 2y = 5 .(-1)
 5x + 2y = 9
-x   - 2y = - 5
-----------------
  4x      = 4
    x = 4/4
    x = 1

x + 2y = 5
1 + 2y = 5
2y = 5 - 1
2y = 4
y = 4/2
y = 2                              S = {( 1 , 2 )}