how to solve this

Question

y=5x-15

-8x-y=-24

solve each system by substitution

Answer 1

The first equation gives you an expression you can use to substitute for the variable y in the second equation as follows:

-8x - y = -24

-8x - (5x - 15) = -24

This is equivalent to :

-8x - 5x + 15 = -24

Now combine like terms and use inverses operations to determine the value of x:

-13x + 15 = -24

-13x + 15 - 15 = -24 - 15

-13x = -39

-13x/-13 = -39/-13

x = 3

Use the first equation to determine the value of y:

y = 5x - 15

y = 5 * 3 - 15

y = 15 -15

y = 0

Therefore the solution to the system of equations is (3, 0)

If you substitute these values into either equation, you will see that x = 3 and y = 0 satisfies both equations.

Answer 2

Just like in Basketball or hockey when you substitute in one player for the other we are going to substitute in one equation in for the other equation.

Given:

Eq 1: y=5x-15

Eq 2: -8x-y=-24

Since Eq 1 is already solved for y, we will use '5x-15' (right side of the '=') in Eq1 for the y value in Eq 2 and solve for x.

-8x-y=-24

-8x -(5x-15) =-24

Note: Don't forget there is a Negative sign in front of the y which means the value of y in Eq 2 is multiplied by -1

-8x – (5x -15) = -24

-8x - 5x +15 = -24

-15 -15

Simplify:

-13x = -39

x= 3

WAIT! We are not done yet. We still need to solve for y.

It doesn't matter which Eq you use but this time use Eq 1 to solve for y, it maybe easier since it is written with y on one side.

Eq 1: y=5x-15

y=5x-15

y = 5(3) -15

y= 0

Answer: x= 3 ; y =0