Question

Solve using the substitution method. Show your work. If the system has no solution or an infinite number of solutions, state this.

-8x – 4y = -68

x + 3y = 16

Answer 1

can you solve that second equation for X ?

Answer 2

first equation should be for x

Answer 3

ok then, what does X equal in the first equation?

Answer 4

sorry, have to go, but someone smarter than I will help you, I am sure

Answer 5

hai there, in this question, you better get the shortest equation which has only 1 variable on 1 side

Answer 6

solving by itself i got 0

Answer 7

what gives 0?

Answer 8

There: x + 3y = 16
This one is the shortest equation, and x seems to be the perfect variable to be forever alone :)
x = 16- 3y

Answer 9

Then you can subtitute this x = 16-3y in the first equation, so you only have 1 variable in the whole equation, makes it lot easier to solve.

Answer 10

so its easier to use the shortest equation first

Answer 11

Yes, if you don't want a huge equation.

Answer 12

i was trying to figure out where you would switch the equation around

Answer 13

Little hint there: -8x - 4y = -68
There's lot of negative there and they could be taken out. 8x + 4y = 68 is much better to look at.
Now all you have to do if to replace x by (16 - 3y) and find y, once you have it, you can get the x

Answer 14

8x + 4y = 68
8(16-3y) + 4y = 68
128 - 24y + 4y= 68
128- 20y = 68
128 - 68 = 20y
60 =20y
y = 3

Answer 15

With this, you can find x easily, knowing y = 3
x + 3y = 16
x + 3(3) = 16
x + 9 = 16
x = 7

Answer 16

It looks really simple if i always get lost on either the second step or don't know when to flip the negative signs.

Answer 17

You can work without changing the signs, but it's just more difficult, when you have something like -a - b = -c, the same thing as a + b = c

Answer 18

There's a proof: http://puu.sh/pQzo

Answer 19

I was using this formula Ax+By=C which is the same that you was using i see. May I'm I'm just being hard on myself cause I know that I know it but haven't used it since I graduated in 2001.

Answer 20

I was using this formula Ax+By=C which is the same that you was using i see. May I'm I'm just being hard on myself cause I know that I know it but haven't used it since I graduated in 2001.