 • 02-26-2003, 06:04 PM
the sherrif
please.. can someone solve my equasion for variable 'c'. Im dieing over this. Even if you cant, please offer some advice. thankyou

im not particulary interested in the answer.. but how to get to it. i already know the answer and it can be found here by pasting in the equasion.

PHP Code:

``` ab-4ca-4cb+12c^2=0  ```
thanko mucho
• 02-27-2003, 03:26 AM
muckyMuckMan
Unless you can see a way to just straight out factor this shiznick, I would use the quadratic formula. Which is what I did.

Just for reminder, the quadratic formula is
Code:

```for the equation ax^2 + bx + c = 0     -b +/- sqrt( b^2 - 4ac) x = -----------------------           2a I will be using the terms "a coefficent", "b coefficent", and "c coefficent" as general coefficents to the quadratic equation above.```
Okay, with that outta tha way.
Code:

```12c^2 - 4cb - 4ca + ab = 0 Start off by finding your "b coefficent". Rewrite your equation as 12c^2 - 4(a+b)c + ab = 0```
Make sense? Reply if it doesn't. I will now continue.

Refer to the above quatratic equation. Now we can say that the "a coefficent" is 12, the "b coefficent" is -4(a+b), and the "c coefficient" (not to be confused with the variable 'c' you're solving for) is ab. With that said, you can now setup the quadratic formula for your equation.
Code:

```    -[-4(a+b)] +/- sqrt( [-4(a+b)]^2 - 4*12*ab ) c = ----------------------------------------------                     2*12     4(a+b) +/- sqrt( 16(a+b)^2 - 48ab ) c = ----------------------------------------------                     24     4(a+b) +/- sqrt( 16[a^2+2ab+b^2] - 48ab ) c = ----------------------------------------------                     24     4(a+b) +/- sqrt( 16a^2 + 32ab + 16b^2 - 48ab ) c = ----------------------------------------------                     24     4(a+b) +/- sqrt( 16a^2 - 16ab + 16b^2 ) c = ----------------------------------------------                     24     4(a+b) +/- sqrt( 16[a^2 - ab + b^2] ) c = ----------------------------------------------                     24     4(a+b) +/- 4*sqrt( a^2 - ab + b^2 ) c = ----------------------------------------------                     24     4 c = -- { a + b +/- sqrt( a^2 - ab + b^2 ) }  Factor out 4/24     24     1 c = -- { a + b +/- sqrt( a^2 - ab + b^2 ) }  Reduce. Answers.     6```
• 02-27-2003, 12:37 PM
the sherrif
ahhhh yessss!!

I completely neglected the quadratic formula. I thought it couldnt be solved using the formula but now its so obvious that

- 4cb - 4ca = - 4(a+b)c

thanks for the reply, its very much appreciated ;)
• 02-27-2003, 05:37 PM
muckyMuckMan
You're welcome. :D