What is y=-6x=7

y=8x-21 in solving system by substitution method?

So,

Notice that y is equal to two different equations.

Since we know that, we can simply put the right sides of both equations side-by-side.

-6x + 7 = 8x - 21

Add 6x to both sides

7 = 14x - 21

Add 21 to both sides

28 = 14x

Divide both sides by 14

2 = x

Substitute in the second equation

y = 8 (2) - 21

Distribute

y = 16 - 21

Collect Like Terms

y = - 5

Check

-5 = - 6 (2) + 7

-5 = - 12 + 7

-5 = - 5 This checks.

Check in second equation

-5 = 8 (2) - 21

-5 = 16 - 21

-5 = - 5 This also checks.

S = { (2,-5) }