2w+3x-12=0 x+5w-13=0 substitution?

Question

how do i work this out, i just don't udnerstand it...

Answer 1

2w+3x-12=0
x+5w-13=0

What you want to do, is use 1 formula to define x in terms of w (or vice versa), then substitute that definition into the other formula.

So, from formula #2:
x + 5w - 13 = 0
x = 13 - 5w

Substitute into formula #1:
2w+3x-12=0
2w+3(13 - 5w)-12=0
2w + 39 - 15w - 12 = 0
-13w + 27 = 0
-13w = -27
w = 27/13 = 2 1/13 (solution for W)

Now substitute the value for w into the formula for x to get the value of x:
x = 13 - 5w
x = 13 - 5 * 27/13 = 13 - 10 5/13 = 2 8/13 (solution for X)

Check:
2 * 2 1/13 + 3 * 2 8/13 - 12 = 0
4 2/13 + 7 11/13 - 12 = 0
0=0 (check!)

Answer 2

rewrite as

2w+3x=12------------(a)
5w+x=13-----------(b)

multiply second equation by 3

2w+3x=12-------------(a)
15w+3x=39-----------(c)

Now, subtract (a) from (c); ie, (c)-(a) u will get
13w=27

or w=27/13

substitute w=27/13 in equation (b)
u will get

x=13 - 135/13