## Mikeyy1992 2 years ago Help? Please and thank you! What is the y coordinate of the y−intercept of the line that passes through the points (−3, −1) and (1, 7)?

1. OpenSessame

-3 -1 1 7|dw:1377494318035:dw|

2. OpenSessame

You have to find the slope of the line!

3. OpenSessame

Slope is...$\frac{ RISE }{ RUN }$

4. Mikeyy1992

Lagging is my life.

5. Mikeyy1992

would that be equal to 1/2 for slope? or no?

6. OpenSessame

Right:)

7. Mikeyy1992

Well, what is my question asking for? the y coordinate?

8. Mikeyy1992

Little confused.-.

9. OpenSessame

Yes! To find where the line crosses the Y axes!

10. Mikeyy1992

-2, 0? Random guess. Lol

11. OpenSessame

$y – y _{1} = m(x – x _{1})$

12. OpenSessame

Now using that formula I gave you plug in one of the Points that are given and solve for y.

13. Mikeyy1992

-1 + 7 = m(-3 + 1)

14. Mikeyy1992

- 7*

15. OpenSessame

Not exactly...Only use one set of points and plug it into the y and x with a tiny 1...

16. OpenSessame

More like... y+1= M(x+3)

17. OpenSessame

And M means slope so plug that in too!

18. Mikeyy1992

y + 1 = 1/2(x + 3)

19. OpenSessame

Yup, now solve for Y.

20. Mikeyy1992

y = 1/2x + 1/2 ?

21. OpenSessame

Yes:)

22. OpenSessame

This form is call slope intercept form. To find y plug in 0 for X.

23. Mikeyy1992

y = 1/2(0) + 1/2 y = 1/2 ?

24. OpenSessame

(0,1/2)

25. Mikeyy1992

Now, this will be tricky to put in the written response, because fractions turn from 1/2 to 12. Lol. Should I just put 0.5?

26. OpenSessame

Wait...before you write it lets check it...cause something doesnt seem right...

27. Mikeyy1992

I feel like it should be a whole number, my teacher said it should be for these ones.

28. OpenSessame

I think is should be (0,5)...

29. Mikeyy1992

@mathstudent55 Maybe they know if we did anything wrong.

30. OpenSessame

I figured out!

31. Mikeyy1992

@Luigi0210

32. OpenSessame

The slope is 2!

33. OpenSessame

we have to redo that with the slope of 2.

34. OpenSessame

Because its Y/X not X/Y.

35. Mikeyy1992

OpenStudy is lagging for me.

36. OpenSessame

Its okay! it is (0,5)

37. OpenSessame

$y+1=2(x+3)$

38. OpenSessame

$y=2x+5$

39. Mikeyy1992

@Luigi0210 I really need to know if he's right. I'm so confused.

40. OpenSessame

Sorry for confusing you...:(

41. OpenSessame

http://www.webmath.com/_answer.php Its right, check...

42. Mikeyy1992

Only if OpenStudy was a real person...

43. Luigi0210

So you're just looking for the y-coordinate of the y intercept?

44. Mikeyy1992

Yes.

45. Luigi0210

Well you know that the y-intercept is when x=0 right?

46. Mikeyy1992

Yes, but now I don't even know what the slope is anymore. 1/2 or 2 or 5 lol.

47. Luigi0210

Slope is: $m=\frac{y2-y1}{x2-x1}$

48. Mikeyy1992

-3, -1 1, 7

49. Mikeyy1992

-1 - 7 ------ -3 - 1 ?

50. Luigi0210

Just plug them in and solve. and either way works, you get the same answer

51. Mikeyy1992

-8 -- -4 ?

52. Luigi0210

Yup, making the slope 2. Now we plug that information into the point-slope formula: y-y1=m(x-x1)

53. Luigi0210

Open was right so far, except for the slope

54. Mikeyy1992

y - 1 = 2(x - 7) ?

55. Luigi0210

Yea, not just distribute.

56. Luigi0210

*now

57. Mikeyy1992

y = 2x - 13?

58. Luigi0210

Yup!

59. Mikeyy1992

Now what?

60. Luigi0210

Now we find the y-intercept Meaning that we plug in where ever there is an x. This will give us the y value we are looking for.

61. Luigi0210

*0

62. Mikeyy1992

What do we use for x? What number?

63. Mikeyy1992

0 = 2x - 3?

64. Mikeyy1992

65. Luigi0210

Ah, plug 0 in for x, not y

66. Mikeyy1992

y = 2(0) - 13 y = -13?

67. Luigi0210

Yup, and that's it Mikeyy :)

68. Mikeyy1992

I feel like that would be one weird y-intercept from where the two dots are on a graph..

69. Luigi0210

Your ordered pair is (-13, 0)

70. Luigi0210

*(0, -13)

71. Mikeyy1992

Alright thanks :P

72. Luigi0210

Mikeyy..

73. Mikeyy1992

Yes?

74. Mikeyy1992

Lol. Answer wasn't -13 but I still got a 88. and I have a chance to get a 90 with my written response...

75. Luigi0210

Yes I was about to say that.. sorry buddy :( I just realized that we used the wrong points for the point-slope formula.

76. Luigi0210

The answer was actually (0, 5) and the equation was y=2x+5

77. Mikeyy1992

It's fine. I had to get over a 60 and I did. So, I'm happy. I need to get off OP before it screws me another time. thanks again

78. Luigi0210

Alright, and you're welcome :)