Question

I'm stuck on how to do this. I know how to use the substitution method, but I've never seen a problem with a number before the y!

x+3y=-3 and 9y= -3x-9. Can anyone show me how to at least start this problem? Thanks!

Answer 1

x + 3y = -3
x = -3y - 3

you with me so far ?

Answer 2

yes :)

Answer 3

you subtracted the 3y and added it to the other side

Answer 4

now we will sub -3y - 3 in for x in the other equation

9y = -3x - 9
9y = -3(-3y - 3) - 9 --- distribute through the parenthesis
9y = 9y + 9 - 9 -- subtract 9y from both sides
9y - 9y = 9 - 9
0 = 0

if your answer comes out equal, with no variables, then there is INFINITE SOLUTIONS

Answer 5

Thank you for explaining! The 9 in front of the y was throwing me off. I really appreciate your help :)

Answer 6

anytime :)

Answer 7

you just mainly want to isolate a variable and then sub that in. it was easy to isolate x because it was by itself.

Answer 8

9y = -3x - 9 -- divide by 9
y = -3/9x - 9/9
y = -1/3x - 1
you could have also subbed in -1/3x - 1 in for y to find x, but you would have to deal with fractions then.

Answer 9

so I do the same thing for every problem? Like if I have x+y=-3 I'd change it to x=-3-y?

Answer 10

yes

Answer 11

or y = -3 - x

Answer 12

Awesome, sounds easy enough :)

Answer 13

you will get the hang of it, then you will be helping others to understand it.

Answer 14

hopefully :) thanks again for your help

Answer 15

anytime :)