Solve the following system of equations, using the substitution method:4x - 5y =3 / 8x = 15 = -24

Question

Solve the following system of equations, using the substitution method:

4x - 5y = 3
8x + 15y = - 24

 

Answer 1

4x - 5y = 3

8x + 15y = -24

multiply the top equation by 2 on both sides

8x - 10y = 6

8x + 15y = -24

add 10y to both sides in the top equation and subtract 15y from both sides in the bottom equation

8x = 6 + 10y

8x = -24 - 15y

see how the left sides of the equations are both 8x?  the same?  that means the right sides are the same too, so we can do this:

6 + 10y = -24 - 15y

25y + 6 = -24

25y = -30

y = -30/25

y = -6/5

4x - 5y = 3

4x - 5(-6/5) = 3

4x + 6 = 3

4x = -3

x = -3/4

Answer:  x = -3/4, y = -6/5