## AonZ Group Title I forgot how to factorise this! :( 3x^2 +2xy - 8y^2 - 8x +14y-3 one year ago one year ago

1. ilfy214

Is this your equation? $3x^2 +2xy - 8y^2 - 8x +14y-3$

2. AonZ

yes

3. ilfy214

Sorry, I was trying to get my question answered.. Anyways! What do we know? We know that the following can be factored out: $x^2$$8y^2$$14$ I left out 3 and why because they can only be only be factored out by 1.

4. ilfy214

Not "why". I meant "y"

5. AonZ

umm ok...

6. ilfy214

Am I not making any sense? damn

7. AonZ

for some reason i cant factorise this question :/ i dont see taking out these common factors to be any help...

8. AonZ

i know its possible to factorise this but i ahve no idea how http://www.wolframalpha.com/input/?i=factorize+3x%5E2+%2B2xy+-+8y%5E2+-+8x+%2B14y-3

9. ilfy214

It will! Promise.

10. AonZ

umm, what method of factorising is this?

11. ilfy214

REVERSE FOIL Starting with 3x^2 and 8y^2, what can they be factored into?

12. ilfy214

3 and 1, x and x 2 and 4, y and y

13. AonZ

14. ilfy214

$3x \times x = 3x^2$$2y \times 4y = 8y^2$ Is that not correct?

15. AonZ

yes thats correct

16. ilfy214

But its a negative so $-4y \times 2y = -8y^2$

17. AonZ

ok

18. ilfy214

But really from that link you posted, you can take out $(x+2y-3)$ From the this you can take out x $3x^2 + 2xy - 8x$ From this you can factor out 2y $2xy - 8y^2 +14y$ And lastly -3$-3$

19. ilfy214

...."you can factor out"....

20. ilfy214

I guess you can I tried to find the greatest common factor in each, instead of reverse foil. Reverse FOIL is mostly for trinomials..

21. AonZ

mhm i tried that. Btw i never done reverse foil before so is there any other way?

22. AonZ

is it possible if you find the greatest common factor?

23. ilfy214

Yes. I just showed you... Also some methods are: - Number of Terms - Factor Out the GCF First - Reversing FOIL - Guess and Check

24. ilfy214

Its possible because that is what I did. For your x, you can factor out x ONLY because 3 is not a factor of 8. Also the lowest variable is x in all three. $3x^2+2xy−8x$

25. AonZ

|dw:1376184367770:dw|

26. ilfy214

you forgot to completely factor out $( 8x^2 - 14y)$

27. AonZ

|dw:1376184611607:dw|

28. ilfy214

Also, this equation is an alternate form of your polynomial, not your polynomial factored out... Besides did you mean to write this instead?$x (3 x+2 y-8)+(14-8 y) y-3$

29. AonZ

mhm yea

30. ilfy214

Its okay :)

31. ilfy214

Lets try this again! Take out your GCF from your polynomial.... $3x^2 +2xy - 8y^2 - 8x +14y - 3$

32. AonZ

not sure how...

33. ilfy214

X, Y and your constant are separate cases. Like what I wrote if you scroll up.

34. ilfy214

Let me try again! Here is your GCF, right? $(x+2y − 3)$ When it comes to your x variables, only x can be factored out since 3 is not a factor of 8 even thought 2 is. Also you can't factor out x^2 because each monomial does not x^2. They all have at least one. $3x^2 + 2xy − 8x$ Also these monomials are the only ones with an "x"

35. AonZ

still dont get how you got ur GCF...

36. ilfy214

When it come to your y variables, you can factor out 2y because 2 is the greatest common factor. $2xy−8y^2+14y$ And lastly for -3. It is the only constant. So when factoring, all you will use is (1) (-3) $−3$

37. ilfy214

Do you know what the term GCF is? GREATEST COMMON FACTOR

38. AonZ

yea... but how did you get it...

39. ilfy214

I thought I just showed you and explained it to you..

40. ilfy214

EXAMPLE: What are the factors and GCF for these numbers? 2 - 1, 2 3 - 1, 3 12 - 1, 2, 3, 4, 6, 12 The GCF for these is 1.