How would you break down these equations to solve for m and b?

9=-3m+b
4=-m+b


Thank you.

Quote:

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Originally Posted by phoenirius

How would you break down these equations to solve for m and b?

9=-3m+b
4=-m+b


Thank you.

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OK I'll show you the first bit, its simple TAKING AWAY!
9=-3m+b
9+3m=b
Now you can finish from here.

-3m + b = 9, can be re-written b = 9 + 3m

and, -m + b = 4

Now sub for b, b = 9 + 3m:

-m + b = 4

becomes

-m + (9 + 3m) = 4
- m + 3m = 4 - 9
2m = -5
m = -2.5

Now solve for b:
-m + b = 4
-(-2.5) + b = 4
2.5 + b = 4
b = 1.5

Therefore, m = -2.5 AND b = 1.5

I was given answers in fractions and when I tried to solve it out I wasn't getting those answers, I thought I was wrong and way off. Thank you for helping me out and giving me a laugh at not seeing it sooner.

First, multiply one of them by -1 to make the b's cancel:

-1(9=-3m+b) ---> -9 = 3m - b
4=-m+b ---> 4 = -m + b

Combine like terms and get: -5 = 2m
Divide by 2 and get m = -5/2
Plug this back in to one of the original equations and solve for b:

4 = -(-5/2) + b
4 = 5/2 + b
4 - 5/2 = b
3/2 = b

Hi, phoenirius,
Do you know how to check your answers?
Substitue the answers you get back into the first equation, see if it's true.
Then, substitue the answer into the second equation, see if it's true.
If both are true, then you have the correct answers.