## anonymous 3 years ago x^2-9x+20 factorise quadratics

1. anonymous

2. anonymous

no :(

3. cwrw238

this one can be factorized

4. hartnn

can u factorize @Raeee_009 ?

5. hba

Quadratic formula $x=-b \pm \sqrt{b^2-4ac}/2a$

6. anonymous

$x = \frac{ -b \pm \sqrt{b ^{2}-4ac } }{ 2a}$ this is the quadratic formula now look at your equation it's x^2-9x+20 so a =1 ,b = -9 , c = 20 just plug in values you will get 2 values of x

7. anonymous

that is so confusing

8. cwrw238

9. cwrw238

to find a and b you need the product ad = +20 and sum = -9 can u think of 2 numbers which fit this requirement?

10. cwrw238

* product ab = + 20

11. anonymous

hmm.. still don't get it :(

12. cwrw238

20 = -4 * -5 right?

13. anonymous

yeah

14. cwrw238

and -4 + -5 = ?

15. hba

|dw:1353601861741:dw|

16. anonymous

-9

17. cwrw238

so thats your values of a and b hba has illustrated the process in his drawing

18. anonymous

ohh im understanding a bit now so is the answer (x-4) (x+9)

19. cwrw238

yea

20. hba

@cwrw238 No.

21. cwrw238

hba - your method is slightly different to mine - true

22. hba

23. anonymous

(x-4)(x-5)

24. cwrw238

oh yes - i misread it (x - 4)(x - 5) is correct solution a = -4 and b = -5 raee_009

25. hba

@Raeee_009 Please see my illustration and try to learn ? Where are you getting confused ?

26. anonymous

ohhhh! i get it now! thank you so much eveyone

27. hba

Your'e welcome.

28. anonymous

one quick question does a + and - = - ?

29. hba

Well (+)(+)=+ (+)(-)=- (-)(-)=+ Got it ?

30. anonymous

ohh yeah thanks :D

31. anonymous

so would x^2-6x-7=(x-7)(x+1)

32. cwrw238

right

33. hba

|dw:1353603740199:dw| @Raeee_009 Awesome :D