Question

What is \left \{ {{7x-9y=-30} \atop {-3x-6y=3}} \right using substitution

Answer 1

`x=-2(9)/(23) , y=(16)/(23 )`

Explanation:

7x - 9y = -30 ------ equation (1)

-3x - 6y = 3 ------ equation (2)

From equation (2),

3x + 6y = -3

x + 2y = -1

∴ x = -2y - 1 ------ equation (3)

Substitute equation (3) into equation (1):
7(-2y - 1) - 9y = -30

-14y - 14 - 9y = -30

-23y = -16

23y = 16

∴ y =
`(16)/(23)`

Substitute y =
`(16)/(23)` into equation (3):

x = -2(
`(16)/(23)`) - 1

= -
`(32)/(23)` - 1

= -
`(55)/(23)` = -
`2(9)/(23)`