• Mar 25th 2007, 11:10 AM
Mathfailure
I have the equation -2x^2+3x+7=0

So using the quadratic forumla I have

-3 plus or minus sqrt(3^2-4(-2)(7))/-4

= -3 plus or minus sqrt(65)/-4

Now, in the solutions manual it has the solutions as

(3 - sqrt(65))/4 , (3+sqrt(65))/4

Just wondering, but why did the denominator of the solutions become positive? and why did the the 3 also become positive? Thanks!!!

Thanks
• Mar 25th 2007, 11:30 AM
Jhevon
Quote:

Originally Posted by Mathfailure
I have the equation -2x^2+3x+7=0

So using the quadratic forumla I have

-3 plus or minus sqrt(3^2-4(-2)(7))/-4

= -3 plus or minus sqrt(65)/-4

Now, in the solutions manual it has the solutions as

(3 - sqrt(65))/4 , (3+sqrt(65))/4

Just wondering, but why did the denominator of the solutions become positive? and why did the the 3 also become positive? Thanks!!!

Thanks

the solutions manual multiplied the answers by -1/-1 (which is 1 so it doesn't change anything).

alternately, the solutions manual could multiply the original equation through by -1 to get the coefficient of x^2 positive (that is, the equation becomes 2x^2-3x-7=0). doing that, you would get the solution the manual has right off the bat