Question

How do you solve this set of linear equations: `9x - 2y = 11; 5x - 2y = 15`?

Answer 1

`x = -1 and y = -10`

Explanation:

`9x-2y = 11" and "5x -2y = 15`

Notice that there is `-2y"` in each of the equations.

Make `2y" "`the subject in each case.

`2y = 9x-11" and "2y = 5x-15`

`color(white)(xxxxxxxxx)2y = 2y`

`color(white)(xxxxx)9x-11 = 5x -15`

`color(white)(xxxxx)9x -5x =-15+11`

`color(white)(xxxxx.xxx)4x = -4`

`color(white)(xxxxxxxxx)x=-1`

`2y = 9x-11" "larr` substitute `-1 " for "x`

`2y = 9(-1)-11`

`2y = -9-11`

`y = -20/2`

`y = -10`