# simultaneous equations urgant for homework

• Apr 15th 2007, 06:14 AM
vtaylor
simultaneous equations urgant for homework
simultaneous equations

x + 2y = 4
3x - 4y = 7
• Apr 15th 2007, 06:21 AM
earboth
Quote:

Originally Posted by vtaylor
simultaneous equations

x + 2y = 4
3x - 4y = 7

Hello,

there are a lot of different ways to solve such a system of equations. Here is one:

A: x + 2y = 4 ===> x = 4 - 2y
B: 3x - 4y = 7 Now plug in the term for x from equation A:

3(4 - 2y) - 4y = 7
12 - 6y -4y = 7

-10y = - 5
y = ½ Plug in this value into equation A:

x = 4 - 2*½ = 3
• Apr 15th 2007, 06:43 AM
Soroban
Hello, vtaylor!

Another method . . . "Elimination"

Quote:

. . .x + 2y .= .4 .[1]
. . 3x - 4y .= .7 .[2]

Multiply [1] by 2: . 2x + 4y .= .8
. . . . . . Add [2]: . 3x .- 4y .= .7

And we have: . 5x = 15 . . x = 3

Substitute into [1]: .3 + 2y .= .4 . . y = ½

• Apr 15th 2007, 06:51 AM
earboth
Quote:

Originally Posted by vtaylor
simultaneous equations

x + 2y = 4
3x - 4y = 7

Hello,

next method:

x + 2y = 4 ===> y = -½x + 2
3x - 4y = 7 ===> y = 3/4x - 7/4

These terms of y must be equal:

-½x + 2 = 3/4x - 7/4
-5/4x = -15/4
x = 3 Plugin this value into the first equation:
y = -½*3 + 2 = ½
• Apr 15th 2007, 09:19 AM
rj2001
good review this is on my final next week