How do yougerssolve the system by substitution. y=-3x-7 y=x+9

Question

I need the step by step equation

Answer 1

Both of these equations have the variable y isolated. The substitution property states the equivalent expressions can be used interchangeably in other expressions. In this case the first equation states that y and the algebraic expression -3x - 7 are equivalent. Instead of using y in the 2nd equation, replace it with -3x - 7.

-3x - 7 = x + 9 (substitution property of equality).

-4x = 16

x = 16/-4 = -4

Does that value for x make both equations true?

y = -3(-4) - 7 = 12 - 7 = 5

y = (-4) + 9 = 5

Yes.

If you graph both the equations on Desmos you will see that the point of intersection of the two lines is (-4,5).

desmos.com/calculator/jmn5p6h31n

You can visit this graph by selecting the URL, right-clicking and selecting "go to...".