So, since y= -7x + 15, and it also equals 5x - 9, you can take what y equals (either one works in this scenario) so lets take the 5x - 9. since this is what y equals, you can take that expression and replace y with it in the other equation. After you do this you'd get 5x - 9 = -7x + 15. Now both sides of this equation are equal to y. To find the solution, you solve for the variable. After you do this, you get x = 2. Now that you know what x is, you can plug that into any of the original equations to find y. lets use y = 5x - 9 again. This time, substitute x with the number you found earlier, 2. Then you solve. It should look like this: y = 5(2) - 9. So y is 1. There is your answer, x = 2, y = 1.
You know that y = y because no matter what y equals, it will just be equal to itself. Since y = y, you can set those two expressions equal to each other.
-7x + 15 = 5x - 9 Add 7x to both sides 15 = 12x - 9 Add 9 to both sides 24 = 12x Divide both sides by 12 2 = x
So, now choose one of the original equations (I'll go with y = 5x - 9 because there are no negatives) and plug the newfound x value (2) into it.
y = 5x - 9 Plug in the x-value y = 5(2) - 9 Multiply y = 10 - 9 Subtract y = 1
Now, to check.
y = -7x + 15 Plug in the values 1 = -7(2) + 15 Multiply 1 = -14 + 15 Add 1 = 1
y = 5x - 9 Plug in the values 1 = 5(2) - 9 Multiply 1 = 10 - 9 1 = 1
