Question 699551: 5a-b=12
7a-3b=20
find a and b.
Answer by Simnepi(216)   (Show Source):
You can put this solution on YOUR website! 5a-b=12 call this Equation (1)
7a-3b=20 call this Equation (2)
to solve this we rearrange one of the equations, let's do equation (1).
Rearranging (1) gives
-b=12-5a Let's change the signs of each term (this is the same as multiplying everything by -1) giving
b=5a-12 let's call this equation (3)
Substitute this value into equation (2) giving
7a-3*(5a-12)=20 multiplying out the bracket gives
7a-15a+36=20
simplifying this gives
-8a=-16
thus
a=2
Now we have a value for a we can use this to work out b
substitute a=2 into one of the equations (1), (2) or (3)
(3) seems the simplest one so we'll use that.
b=5*2-12
therefore
b=-2
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