I've tried this more than five times but i'm still unsure if it's a No Solution or not.

Question

I've been stuck on this substitution problem for a while now:

3x-y=-25

4x+2y=-20

But I'm still unsure. I've done it enough to know that x= 1, but then it gets confusing. Could anyone help me with this?

Answer 1

Hi Bryant,

You can use elimination to solve this pair of equations.

3x - y = -25

4x + 2y =-20

Multiply the first equation by 2 so that you can combine the two equations and find the value of x first:

3x - y = -25 becomes 6x - 2y = -50

4x + 2y =-20 4x + 2y = -20

10x = -70

10x /10 = -70/10

x =-7

Now substitute -7 for x in either equation and solve for y (I'll use the equation 4x + 2y = -20):

4x + 2y = -20

4 • (-7) + 2y = -20

-28 + 2y = -20

-28 + 2y + 28 = -20 + 28

2y = 8

2y/2 = 8/2

y= 4

The solution for these two equations is (-7,4); x will be -7 and y will be 4