## anonymous 5 years ago 3x-7y=21. Need the 3 ordered pairs where #1: x=0, is __ #2: y=0, is __ #3: y=-6, is __.

1. anonymous

ok, so for the first one, you would plug in 0( which is x) in the equation.: 3(0)-7y=21 0-7y=21 y=21/-7 y=-3, so first ordered pair would be (0, -7) for the second one you would plug in0 for y this time, and in the third one you would plug in -6 for why, and solve for x on that too. then you have your three ordered pairs

2. anonymous

I am still not getting it so need more help

3. anonymous

ok, so lets do the second one

4. anonymous

ok i tried but got lost

5. anonymous

the second one says y= 0 so we are going to plug in 0 for the y, in the function: 3x-7y=21 so when we plug in 0 for y, the function now says: 3x-7(0)=21 next we multiply 0 times 7, so we get: 3x-0=21, which is basically 3x=21 next, we finaly divide 3 on both sides to get x by itself x=21/3 which is x =7

6. anonymous

so now that we know that x=7 , when y=0, the ordered pair is in the form of (x,y) which in this case, it would be (7, 0). that is your second set of points. did you understand this?

7. anonymous

well when i did it it was a little different but it did not look right but had the same answer

8. anonymous

for the last one i started with 3x-7(-6)=21

9. anonymous

10. anonymous

ok wait a sec

11. anonymous

whats -7 *-6?

12. anonymous

don't I replace the y with -6?

13. anonymous

yes, but what is -7 times -6. can you hold up for a sec

14. anonymous

sure

15. anonymous

3x-7(-6)=21 is the correct next step, but what do you get when you multiply negative 7 times negative 6?

16. anonymous

you get positive 42

17. anonymous

so you should have 3x-42=21

18. anonymous

no, its going to be 3x+42=21 because we got positive 42, not negative 42

19. anonymous

ok i see

20. anonymous

yes 3x+42=21, what do we do next?

21. anonymous

get x by itself by using 3

22. anonymous

OK WAIT

23. anonymous

we still have that 42 there, and we need to get rid of it, so how do we get rid of that 42: 3x+42=21

24. anonymous

3x +42 -42 = 21 +42 - 42

25. anonymous

there we go! and what do we get?

26. anonymous

3x=21

27. anonymous

wait whats 21-42? -21!

28. anonymous

huh?

29. anonymous

I thought the 42s cancelled each other out

30. anonymous

yes, but its not 3x=21 its 3x=-21

31. anonymous

ok I don't get it

32. anonymous

so this is what you got 3x +42 -42 = 21 +42 - 42

33. anonymous

right

34. anonymous

why did you add 42 both sides? you were only supposed to subtract 42 on both sides. try it again,

35. anonymous

3x +42 -42 = 21- 42 is what you should get

36. anonymous

ok i put an extra one in there

37. anonymous

exactly so figure it from this: 3x +42 -42 = 21- 42

38. anonymous

ok so 3x +42 -42 = 0

39. anonymous

21 -42= -21

40. anonymous

yes so it should be 3x=-21

41. anonymous

so (-21,-6) is the ordered pair

42. anonymous

we stil need to find x! we were left with 3x=-21 ! remember we need to get x by itself!

43. anonymous

ok so we us 3 on both sides

44. anonymous

we divide 3 by both sides

45. anonymous

damn this thing hangs up on me a lot. so we should end up with x = 21

46. anonymous

whats -21/3?

47. anonymous

-7

48. anonymous

so x=-7. gosh, what grade are you in? and math level?

49. anonymous

I just started college last year Oct and I graduated in 1969 and had just basic math. I was able to transfer 52 credits from my military career. So I am about a late sophmore or early junior. math is 092 which is pre algebra

50. anonymous

college 0.0i learned this in 6th and 7th.

51. anonymous

ya I know but I have never had algebra before

52. anonymous

and im in 9th. yaaay! i feel so smart!

53. anonymous

when i was in high school we did not have algebra and geometry. it did not exist

54. anonymous

so when i was in 12th they were just starting it as an elective.

55. anonymous

I guess that is why it is so hard for me.

56. anonymous

whoa! it really does amaze me how far human intelligence has gone. I cant imagine how advanced our human race will be in he next 40 years

57. anonymous

ya i know. i wish there was a way for me to shock the heck out my brain so it would be easier for me to learn

58. anonymous

lol, so do i! agh sooo much work!

59. anonymous

ya but you understand this. I son't understand any of it. I just started in Jan to learn this junk

60. anonymous

ya, this si easy. but im doing precal, and ap microecon, and ap Human Geogarohy, and ap bio