## denise9423 3 years ago Can someone plz help me get started on these fractions f(x)=3x-8 div 4x+20

1. AsianDuck

What do you need?

2. saifoo.khan

$\frac{ 3x - 8}{4x + 20}\to \frac{3x-8}{4(x+5)}$As there is nothing common between denominator and numerator so we cannot simply it.

3. denise9423

sorry I just found this.

4. saifoo.khan

No worries! :D

5. denise9423

How do I find the domain

6. denise9423

hi

7. Akshay_Budhkar

domain is all real numbers except for -5

8. brinethery

No division by zero. So what is x going to be when the denominator is zero?

9. denise9423

0

10. saifoo.khan

set the denominator equal to zero right? @Akshay_Budhkar

11. brinethery

no. x cannot = -5.

12. Akshay_Budhkar

Yes @sai

13. Akshay_Budhkar

@saifoo.khan

14. denise9423

f(x)=3x-8 over 4x+20

15. brinethery

@denise9423 Domain means all of the values x can take on. Here's your domain: $x \neq-5$

16. Akshay_Budhkar

If you have a look the function is having real values for all values except for x=5 when it is not defined as the denominator is zero

17. denise9423

can you show me how to get 5

18. brinethery

4x+20 =0 Solve for x. x=-5.

19. brinethery

Do you know why division by zero is not allowed?

20. denise9423

ok,then can i sub it also 3x-8

21. brinethery

no!

22. brinethery

you only need to worry about the bottom.

23. denise9423

no to ur question ok

24. brinethery

Remember this: What is 1 divided by 0? In other words, what times zero can equal 1? 0*2? 0*3? There is nothing you can multiply by zero to get 1. So whenever you get these fractions and they ask you to find the domain, just think about what x has to be in order for the denominator to equal zero.

25. brinethery

If you have an equation in the denominator, then set that equal to zero :-)

26. brinethery

*and solve for x.

27. denise9423

like this 4x+20=0

28. brinethery

Yup! :-)

29. denise9423

ok

30. brinethery

Or if you have 1/(x^2+2x+3) . If you have something weird like that, then set it equal to zero and use the quadratic formula to solve for your two x-values. Those x-values are what x can't equal. Sorry, I sound like I'm talking in riddles lol.

31. denise9423

ok so -7xyy over 28xxxxxy=0

32. brinethery

Are you in algebra?

33. denise9423

yes and Its rough

34. brinethery

I'm gonna be more specific with what I said, sorry my fault: Or if you have 1/(x^2+2x+3) . If you have something weird like that, then set it equal to zero and use the quadratic formula to solve for your two x-values. Those x-values are what x can't equal. Sorry, I sound like I'm talking in riddles lol. x^2+2x+3 = 0 (then use the quadratic formula and solve for x)

35. brinethery

That's okay!

36. brinethery

I don't think they'll ask you to find the domain of something with x's and y's. Or are they?

37. denise9423

yes

38. denise9423

no sorry

39. denise9423

simplify

40. brinethery

I can help you on something like that, but first off is that denominator stuff making sense? Really sleep on that and try to remember it b/c it's super important for calculus.

41. denise9423

-7xyy/28xxxxxy

42. brinethery

Okay well what multiples to 7 and 8 have in common? What can you divide them both by?

43. brinethery

I mean 28.

44. denise9423

yes it does bc it will help me remember to put=0 so I can solve for x

45. brinethery

good :-)

46. denise9423

4

47. brinethery

-7xyy/28xxxxxy You can divide the numerator and denominator by 7. Also, which has the smallest amount of x's, and then which one has the smallest amount of y's?

48. denise9423

3x7=28

49. denise9423

no 4x7=28

50. brinethery

The numerator has the smallest amount of x's. There is 1 of them. The denominator has the smallest amount of y's, which is 1 y. So we'll divide the numerator and denominator by 7. -1*x*y*y/4xxxxxy

51. denise9423

bottom has 5 x's and the top has 2 y's

52. brinethery

We have to cancel out the smallest amount of x's. And we also cancel out the smallest amount of y's. So we have: -1*y/4xxxx I canceled out an x on the top and bottom. Then I canceled out a y on the top and bottom.

53. denise9423

ok

54. denise9423

sorry i have a 911 gotta chk out b back later thank you for all ur help god bless

55. brinethery

k

56. brinethery

Anyway, -1*y/4xxxx can be re-written as: -y/4x^4 See Paul, my favorite math teacher: (I swear by his notes) http://tutorial.math.lamar.edu/Classes/Alg/IntegerExponents.aspx