how do you solve the following system by substitution4y=-5x , 5x+8y=20

Question

solve system using any method

4y=-5x

5x+8y=20

Answer 1

Substitution method:

4y = -5x

Divide to each side by 4.

4y/4 = -5x/4

y = -5x/4 -------> (1)

5x+8y = 20

From (1) substitute the y value in (1).

5x+8*-5x/4 = 20

5x-10x = 20

-5x = 20

Divide to each side by negitive 5.

-5x/-5 = 20/-5

⇒ x = -4

Substitute the x value in (1).

y = (-5*-4)/4

y = 20/4

⇒ y = 5

Solution is x = -4, y= 5.