• Apr 15th 2009, 07:33 AM
I'm stuck on this one....

6r^2-r-2=0

Any assistance appreciated.

Thanks
Thomas
• Apr 15th 2009, 07:42 AM
masters
Quote:

I'm stuck on this one....

6r^2-r-2=0

Any assistance appreciated.

Thanks
Thomas

Here's a technique you can use.

Multiply the leading coefficient (6) by the constant (-2).

This gives you -12.

The coefficient of the middle term is -1.

You need a pair of numbers whose product is -12 and whose sum is -1.

After thinking a bit on this, you should come up with the only combination that works, namely -4 and 3.

$6r^2{\color{red}-4r +3r}-2$

Now group the first two terms, and then the last two terms.

$(6r^2-4r)+(3r-2)$

Factor each group.

$2r(3r-2)+1(3r-2)$

$(3r-2)$ is a common factor, so

$(3r-2)(2r+1)$

All done.
• Apr 15th 2009, 07:52 AM