Question

How do you solve the system `4x - 3y = 34`, `3x + 9y = -42`?

Answer 1

Using Gaussian elimination, add three times the first equation to the second equation to leave an expression just in `x`. substitute this back into one of the equations to find `y`.

Explanation:

`4x - 3y = 34`
`3x +9y = -42`

Equation `1` times `3` gives
`12x - 9y = 102`

Adding this to equation `2` gives
`15x = 60`

`:. x= 4`

`4*4 - 3y = 34`
3y = 16 - 34 = - 18#

`:. y = -6`