# Thread: [SOLVED] Descartes's Rule Of Signs

1. ## [SOLVED] Descartes's Rule Of Signs

When Doing The Problems... determining and positive or negative real zeros i always get them wrong...

I Just Dont Get It...

Ex.

f(x)= 2x^4-x^3+6x^2-x+5

how is it 4 or 2 or 0 positive real zeros?
None Negatives?

2. Descartes' Sign Rule -- from Wolfram MathWorld

Can you state Descartes's Rule Of Signs ?

3. Originally Posted by Plato
Descartes' Sign Rule -- from Wolfram MathWorld

Can you state Descartes's Rule Of Signs ?
I Can... But Somehow I dont Know How... The Numbers Of Zeros End Up One Less Than The actual zeros...

4. Originally Posted by Plato
Can you state Descartes's Rule Of Signs ?
so in other words yu start counting changes from, lets say from my example: 5?

but why would there be 4 or 2 or 0 positive zeros?

5. Originally Posted by >_<SHY_GUY>_<
but why would there be 4 or 2 or 0 positive zeros?
Well there are four changes in sign.
So there are 4, 4-2=2, or 4-4=0 positive roots.

6. Oh... now i get it!

these texts books are not good at explaining... they use some other method.... it confuses the whole class. and the teacher goes sometimes by the book... thanks!