Posted by **Ashley** on Thursday, January 29, 2009 at 10:01pm.

Solving Systems by Substitution:

2. x=1-4y

2x+7y=3

I need help learning how to do this problem step-by-step

- algebra -
**Reiny**, Thursday, January 29, 2009 at 10:04pm
your first equation says that

x = 1-4y

so "substitute" 1-4y wherever you see x in the other equation

2x+7y=3

2(1-4y) + 7y = 3

2 - 8y + 7y = 3

-y = 1

y = -1

next sub that y = -1 back into the first equation

x = 1 - 4(-1) = 1+4 = 5

- algebra -
**Chopsticks**, Thursday, January 29, 2009 at 10:12pm
x = 1-4y

2x+7y=3

Starting with the first equation

since x = 1 - 4y

Plug that in to the second equation

2(1-4y)+7y=3

2 -8y + 7y = 3

2 - y = 3

2/2 - y = 3/2

- y = 3/2

Since why can't be negative, move the negative over to the other side

y = -3/2

Okay we found what Y is now plug that into the first equation

x = 1-4(-3/2)

x = 1 + 6

x = 7

so the answer is (7,-3/2)

I'm pretty sure this is right, but I hope a real tutor comes and say for sure

- algebra -
**Chopsticks**, Thursday, January 29, 2009 at 10:14pm
Oh sorry, I did my math wrong and Divided instead of subtracting.

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