substitution methon

[marifran]

I am using the method but don't get a whole number for an answer: The equation is 7x-4y=26, y = x-5. I have -4y = -7x + 26 and -7x + 26 = x -5. Subtract the x from 7x and get 8x sub. 26 from both sides and get -31 so I get an answer of x = -31
-8
Is that right?

 

[Aladdin]

You were given : 7x - 4y = 26 & y = x - 5

Solve this system of equation by using Substitution Method :

7x-4(x-5)=26

7x-4x+20=26

3x=6

x=2

Substitute x in the second equation to find y , y=2 - 5=-3

 

[mmm4444bot]

I have -4y = -7x + 26 This shows that you subtracted 7x from both sides. That's okay.

and -7x + 26 = x -5. This shows that you next substituted x - 5 for y, but you forgot the coefficient -4

Hi MariFran:

There's nothing wrong with starting by subtracting 7x from both sides, but it's not really necessary (as shown by Aladdin's work).

Your mistake is dropping the -4 on -4y.

If we substitute the expression x - 5 for y in the term -4y, then we get -4(x - 5).

After you fix your mistake, you'll get the following.

-4(x - 5) = -7x + 26

Now you have an equation that contains only one variable. Journey onward!

Cheers,

~ Mark