math problem help please???

Multiply both sides by 'x'.
3 = 12 + 7x

-9 = 7x
x = -9/7

3/x = 12/(x + 7)
[3(x + 7)]/x = 12
(3x + 21)/x = 12
3x + 21 = 12x
3x - 12x = -21
-9x = -21
x = -21/-9
x = 7/3

. 3 . . . . .12
––– = –––––
. x. . . . .x + 7

3(x + 7) = 12x

3x + 21 = 12x

3x - 12x = -21

-9x = -21

. . . .-21
x = ––––
. . . . -9

. . . . 7
x = –––
. . . . 3

. . . . . .1
x = 2 –––
. . . . . .3

Done

3/x=12/x+7
x(3/x=12/x+7)
3=12+7x
3-12=7x
-9=7x
x=-9/7
Check the answer by replacing -9/7 for x in the Original equation.

3/x -12/x=7
-9/x=7
x=-9/7

You have to cross multiply:

3 = 12
x x + 7

You have to get rid of the xs on the bottom. To do this, you multiply the left fraction by x, and multiply the right fraction by x+7. (Think about it: if you have 1/2, and you want to get rid of the 2 on the bottom to make it one line, you multiply it by 2)

Therefore, you get:

3(x+7) = 12(x)
3x + 21 = 12x (-3x)
21 = 9x
x=2.3333333 (2.3 recurring)


PS - -9/7 is not correct: You can check by substituting -9/7 into the equations: 3/(-9/7) = -2.33333. However, 12/ (-9/7 +7) = 2.1, which doesn't equal the left hand equation (and they have to because of the equals sign.)

However, if you take x = 2.3 recurring, you get:

3/ (2.33333333..) = 12/ (2.3333333....+7)
1.285714286 = 1.285714286

THEREFORE, x = 2.3 recurring =]

3/x = 12/x + 7

x(3/x) = x(12/x + 7)

3 = 12 + 7x

3 - 12 = 12 + 7x - 12

-9 = 7x

-9/7 = 7x/7

-9/7 = x

3/x=12/x+7
1st multiply both sides by x
3=12+7x
2nd subtract the 12 from both sides
-9=7x
3rd divide both sides by 7
-9/7=x

x = -9/7

3/x=12/x+7 times x
3=12+7x minus 12
-9=7x divide by 7
-9/7 = x