-5x^3 + 24x^2 - 36x + 16

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- Apr 11th 2009, 06:10 AMMr RayonFactorise:
-5x^3 + 24x^2 - 36x + 16

- Apr 11th 2009, 06:16 AMstapel
First do the graph in your calculator, so you start your work already having a pretty good idea of where the zeroes are. (Wink)

Then apply**the Rational Roots Test**to obtain a list of*possible*whole-number and fractions zeroes. You should get:

. . . . .$\displaystyle \pm\, \frac{1,\, 2,\, 4,\, 8,\, 16}{1,\, 5}$

Since whole numbers are easier, start trying whole-number solutions, such as -1 and +4, by**synthetic division**.

Once you've found one zero, you can plug the remaining quadratic into**the Quadratic Formula**to complete the solution.

If you get stuck, please reply showing all of your steps so far. Thank you! :D - Apr 11th 2009, 06:16 AMMoo
- Apr 11th 2009, 06:36 AMMr Rayon
What do you mean 2 is a root. How does that help me factorise the above. I don't understand. (Crying)

I'm also not sure what the rational root test and synthetic division are. I'll follow the links and see but I'm pretty sure it's not something that we go through in my math classes. - Apr 11th 2009, 06:48 AMstapel
To learn the relationship between factors and zeroes, try

**here**. (We had assumed that this material had been covered in class before you were required to use the knowledge. Sorry!)

If you're not supposed to use the standard methods (and you must not be, or they would have been mentioned in class and in your book), then please reply with the methods that you are supposed to use. We'll be glad to try to help you with whatever non-standard tools or algorithms they've given you, but you'll first need to tell us what they are. (Wink)

Thank you! :D