## anonymous 3 years ago x intercept for this function

1. anonymous

$\huge y=x^3-9x^2+15x+4$

2. anonymous

this is unfactorable?

3. anonymous

oh no wait nevermind

4. anonymous

Any particular method they want you to use? Do they specify factoring?

5. anonymous

No but isnt that the only way?

6. anonymous

Graphing is the easiest.

7. anonymous

Graph that bad boy. Look for where it crosses the x axis. Doneso.

8. anonymous

no i have to use an algebraic method

9. anonymous

because like say on an exam, i cant graph that

10. Mertsj

Possible rational roots are :

11. anonymous

Okay then your best best is to use the rational root theorem to list possible rational roots. Then check each one to see if it is a valid root.

12. Mertsj

$\pm1,\pm4,\pm2$

13. Mertsj

Use synthetic division to see if any of those are actual roots.

14. anonymous

Mertsj is correct. The way he got those possible roots is: A: Make a list of factors for the last number (In this case, it's 4) B: Make a list of factors for the first coefficient (In this case, it's 1) Possible rational roots must be of the form $$\huge \frac{\text{things in the first list}}{\text{things in the second list}}$$

15. Mertsj

It is not factorable.

16. Mertsj

So the best approach would be to find where y changes sign. Then you would know there is a root between those two values and you could hone in on it by trial and error. Of if you know calculus, you could use the derivative. What class is this for?

17. anonymous

@Mertsj calculus !

18. anonymous

they want you to bruteforce using newton's more than likely