4. Substituting for y:
.. 7x -(6 -2x) = 3
.. 9x = 9 . . . . . . . . . add 6, collect terms
.. x = 1
.. y = 6 -2*1 = 4
(x, y) = (1, 4)
5. Substituting for x:
.. 3(y -4) +y = 12
.. 4y = 24 . . . . . . . add 12, collect terms
.. y = 6
.. x = 6 -4 = 2
(x, y) = (2, 4)
6. Substituting for x:
.. 4(y -5) -y = 4
.. 3y = 24 . . . . . . . add 20, collect terms
.. y = 8
.. x = 8 -5 = 3
(x, y) = (3, 8)
7. y = 2x -6 . . . . . add 2x to the first equation
Substituting for y:
.. 5x -(2x -6) = 9
.. 3x = 3 . . . . . . . add -6, collect terms
.. x = 1
.. y = 2*1 -6 = -4
(x, y) = (1, -4)
8. x = 2 -3y . . . . . add -3y to the first equation
Substituting for x:
.. y -(2 -3y) = -6
.. 4y = -4 . . . . . . . add 2, collect terms
.. y = -1
.. x = 2 -3*(-1) = 5
(x, y) = (5, -1)