Solve the system of equations by substitution if possible

Question

y = 7x - 21

9x - y = 29

Answer 1

You already have y in terms of x from the top equation. Plug that into the place of y in the bottom equation, and solve for x. Then plug the result for x into the top equation and solve for y.

Answer 2

Hey Sam!

Above you will find a video dictating the steps for this problem. Feel free to message me with any questions.

Answer 3

The top equation is already solved for y, so you can substitute 7x - 21 into the second equation for y and solve for x:

9x - (7x -21) = 29

9x - 7x + 21 = 29

2x + 21 = 29

2x = 8

x = 4

Then, substitute x = 4 back into the first equation to solve for y:

y = 7(4) - 21

y = 7

So the solution of the system is (4, 7). You can verify this by plugging x = 4 and y = 7 back into both equations.

7 = 7(4) - 21

9(4) - 7 = 29

Both of the above equations are true so that verifies that your answer is correct. You can also graph the two equations on a graphing calculator and find the intersection point to check your answer.