Posted by **Julie Jam** on Wednesday, December 8, 2010 at 1:11pm.

A. 3x + y = 8

x-y =6

B. x- 1/2y =2

y=2x-4

C. x + 2y = 9

2y = -x + 13

I am not grasping the substitution method! Please help me.

- algebra -
**Reiny**, Wednesday, December 8, 2010 at 1:40pm
Pick the equation for which it is easier to "isolate" one of the variables.

A) from the second: x = 6+y

plug that into the first

3**x** + y = 8

3**(6+y)** + y = 8

18 + 3y + y = 8

4y = -10

y = -5/2

now put that back into the easier of the two

x = 6+y

x = 6 - 5/2 = 7/2

b) really easy, y is already isolated

c) notice we have 2y isolated , but 2y shows up in the first, so again, real easy

x + 2y = 9

x + (-x + 13) = 9

13 = 9 ?????

ahhh, this last pair of equation has no solution, (we got a silly statement)

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