quadratic equation - discrimination

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- Dec 18th 2007, 11:40 PMafeasfaerw23231233quadratic equation - discrimination
quadratic equation - discrimination

- Dec 19th 2007, 01:03 AMmr fantastic
Your expression for the discriminant can be re-arranged into

.

For unequal roots (ie. two distinct roots) you want .

NB (an acronym for the latin phrase*nota bene*which translates as*note well*, that is,*what follows is very important so pay close attention, chum*): We don't give a fetid dingos kidney whether the roots are real or not, as long as they're distinct. So the requirement is , NOT .

Let's assume . Since a is real, then (IF the assumption is true) you can solve*this*quadratic to find real values of a. Therefore (IF the assumption is true) the discriminant of*this*quadratic is greater than zero.

From here, I'll let you fill in the steps that lead to , an impossibility for real values of b and c.

Hence the assumption is false. So . Q.E.D. - Dec 19th 2007, 05:29 AMJaneBennet
You can also write

Since .

Hence*D*is (strictly) positive, so the equation has real and unequal roots.