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Help with this algebra and functions question please?

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I got to part (b) and now I'm stuck. I have a+b = 7 and -8a+4b = 4 and now I don't know how to go about getting the value of a and b
Original post by jessnoch
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I got to part (b) and now I'm stuck. I have a+b = 7 and -8a+4b = 4 and now I don't know how to go about getting the value of a and b


You have two equations. Two unknown values. How do you reduce it to one unknown value?
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Avatar for jessnoch
jessnoch
OP
1
Original post by High Stakes
You have two equations. Two unknown values. How do you reduce it to one unknown value?


I don't know, I think I'm being dumb:frown:
Original post by jessnoch
I don't know, I think I'm being dumb:frown:


If a + b = 7, then a = 7 - b right?

How can I use that information in the other equation?
To get the value of a and b, you have to solve the two equations simultaneously.

The two equations we have are:

a + b = 7 and -8a + 4b = 4.

Rearrange the first equation to make a the subject.
a = 7 - b

Subsitute the rearranged equation into the second equation of -8a + 4b =4.

-8(7 - b) + 4b = 4

Simplify This subsitution to solve for b by expanding the brackets:

-8(7 - b) + 4b = 4 = -56 + 8b + 4b = 4

Now solve for b( collecting like terms)
(move the -56 to the other side to get +56 so that makes 12b = 60
12b = 60
b = 5

Subsitute b = 5 into any of the equations to find the value of a:

a = 7 - (5)
a = 2

So you values for a and b are:

a = 2 and b = 5.
Reply 5
Avatar for Notnek
Notnek
21
Original post by crystala1998
...

Please don't post full solutions - it's against the rules of this forum.

The first half of your post would have been great to allow the OP to finish it themselves.

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