Okay I was doing well until I stumbled across a question that was backwards if that makes sense.

Like:

a+4b=15

5b=2a+3

or

5=2y-x

7=3y-2x

I have been trying at those two for over an hour.

Please help!

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- March 19th 2008, 06:46 PMristeekHelp with solving linear systems by substitution
Okay I was doing well until I stumbled across a question that was backwards if that makes sense.

Like:

a+4b=15

5b=2a+3

or

5=2y-x

7=3y-2x

I have been trying at those two for over an hour.

Please help! - March 19th 2008, 06:58 PMristeek
Listen I have been this for 5 hours straight I am a poor math student but I try. My teacher is rude and ignorant. Please if it is not to much trouble a little help please. Currently I have no patience. (Headbang)

- March 19th 2008, 07:35 PMMacleef
I'll do the first one.

(1) a+4b=15

(2) 5b=2a+3

Isolate for either "a" or "b" in (1) or (2).

I'll isolate for "a" because it's easier.

(1) a = 15 - 4b

(2) 5b = 2a + 3

Now, substitute (1) into (2) to find "b"

5b = 2a + 3

5b = 2(15 - 4b) + 3

5b = 30 - 8b + 3

Isolate for "b"

5b + 8b = 33

13b = 33

b = 33/13

Now, substitute "b = 33/13" into (1) or (2) to find "a"

a = 15 - 4b

a = 15 - 4(33/13)

a = 15 - 132/13

Need a common denominator

a = (195 - 132)/13

a = 63/13