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Old 03-31-2008, 05:05 AM   #1
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Default help!

hey

well.. i go back to school this week.. and i have some homework to do..

HOORAY

anyway.. ive forgotten it, so could you guys help me out???

just explain this algebra for me and it will spring back in my mind... hopefully

Expand:
(3x+2)(x+4)

please run me through the answer
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Old 03-31-2008, 05:08 AM   #2
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Default Re: help!

Assuming that im correct,im not all that good at algebra but ill give it a shot:

1 X on it's own equals 1,therefore 3x = 4,So 4 +2 equals 6.

and X + 4 would equal 5,So 6 + 5 equals 11
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Old 03-31-2008, 05:08 AM   #3
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Default Re: help!

i think it is 3x= 3x3 and x plus 4 it think will be 3x3 =x and then add 4 to that answers your answers i think is 13.
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Old 03-31-2008, 05:11 AM   #4
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Default Re: help!

Quote:
Originally Posted by !"£$%^&*() View Post
i think it is 3x= 3x3 and x plus 4 it think will be 3x3 =x and then add 4 to that answers your answers i think is 13.
im asking a 5 year old?? NO

and i just need it expanded, no answers
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Old 03-31-2008, 05:12 AM   #5
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Default Re: help!

Try This then http://www.algebra.com/
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Old 03-31-2008, 05:32 AM   #6
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Default Re: help!

tried.. FAILED lol..
and yeh....
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Old 03-31-2008, 08:06 AM   #7
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Default Re: help!

(3x+2)(x+4)

FOIL - First Inside Outside Last

first 3x * x = 3x^2
Outside 3x * 4 = 12x
Inside 2 * x = =2x
Last 2 * 4 = 8


then add them all together

3x^2 + 12x + 2x + 8

= 3x^2 + 14x + 8

--------------------------------------------------------------------------------------------
and now to move onto the answers given above...

you can't find an answer (the answer is not 11 and it's not 13) also 1x = x not 1 since x is a number, it could be any number (e.g if x=10 1*10 is not 1)


if you were given the problem (3x+2)(x+4) = y, x = 2 find y then you could have an answer

(3*2 + 2)(2 + 4)
(6 + 2)(6)
8*6 = 48, y=48

or if you were given the problem (3x+2)(x+4) = 48 find x

then you'd do

(3x+2)(x+4) = 48

expand the brackets as above
3x^2 + 14x + 8 = 48

subtract 48 from each side
3x^2 + 14x + 8 - 48 = 0

simplify
3x^2 + 14x - 40 = 0

that's a quadratic equation

quadratic equations can be solved either by graphing the equation, and you find where the graph crosses 0 on the x axis

or by using the quadratic equation formula.
quadratic equations come in the form ax^2+bx+c = 0

the formula for solving them is
x = -b +- sqrt(b^2-4ac) / (2a)

(quadratic equations have two possible answers as a x^2 graphed is a curve that will intercept the x axis twice (unless x=0 then it'll only cross the x axis once at x=0))

in this case

x = -b +- sqrt(b^2-4ac) / (2a)
a = 3
b = 14
c = 40


x = [-14 +- sqrt(14^2 - 4*3*-40)] / 2*3

x = [-14 +- sqrt(196 - -480)] / 6

x = [-14 +- sqrt(196 + 480)] / 6

x = [-14 +- sqrt(676)] / 6

x = [-14 +- 26] / 6


so x = [-14 + 26] / 6 = 12/6 = 2
or x = [-14 - 26] / 6 = -40/6 = -6.66666(recurring)




Hopefully that'll have cleared it up for you...
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Old 03-31-2008, 02:31 PM   #8
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Default Re: help!

He never said the equation was equal to 0 though. Ignore everything after the dashed line in root's post.

The answer is 3x^2 + 14x + 8 though, as root said, you use FOIL.
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Old 03-31-2008, 04:40 PM   #9
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Default Re: help!

What he said ^^^^^.

Then if the equation is equal to 0, you use quadratic.

"FOILing" is the easy part. Wait till you get to factoring, which takes some trial and error for a while. I've gotten used to it so I just do by head =]
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Old 03-31-2008, 04:59 PM   #10
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Default Re: help!

Factoring sucks ^_^
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