## burhan101 2 years ago x intercept for this function

1. burhan101

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

2. burhan101

this is unfactorable?

3. timo86m

oh no wait nevermind

4. SmoothMath

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

5. burhan101

No but isnt that the only way?

6. SmoothMath

Graphing is the easiest.

7. SmoothMath

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

8. burhan101

no i have to use an algebraic method

9. burhan101

because like say on an exam, i cant graph that

10. Mertsj

Possible rational roots are :

11. SmoothMath

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. SmoothMath

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. burhan101

@Mertsj calculus !

18. oldrin.bataku

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