How do you do the Descartes rule of signs?

Question

askme12345 · Answer

substitute all your x's for negative x :)

anonymous · Answer

Will you show me an example please?

anonymous · Answer

first count the sign changes in the original polynomial, the compute f(-x) and count the sign changes

askme12345 · Answer

Sure - 
Lets say your equation is -5x^3 + 4x^2 - 5x
So you have negative, positive, negative = this means 3 positive zeros (when youre solving for zeros)
decartes rule says when you put -x into the equation you'll get your negative zeros .. here we go
-5(-x)^3 + 4(-x)^2 -5(-x) (All even powers, will become negative, odds stay the same)
5x^3 - 4x2 + 5x .. so we have postive to negative to positive .. therefore 3 positive zeros

anonymous · Answer

purplemath has a good example and explanation

anonymous · Answer

http://www.purplemath.com/modules/drofsign.htm

anonymous · Answer

Thanx for the help! XD