## RealityWillSlapYou Group Title Select the equations that are parallel and perpendicular to y = −3x − 1 and that pass through the point (3, 1). A. parallel: y = −3x + 6 perpendicular: y = (1/3)x + 2(2/3) B. parallel: y = −3x + 10 perpendicular: y = (1/3)x C. parallel: y = -(1/3)x perpendicular: y = −3x D. parallel: y = (1/3)x + 1 perpendicular: y = 3x − 1 one year ago one year ago

1. RealityWillSlapYou Group Title

@SmokeysTheName, Right here!

2. SmokeysTheName Group Title

ohhh man, remember i said i couldn't help? but here @phi might be able to

3. RealityWillSlapYou Group Title

Oh, oops! Sorry about that.... :)

4. SmokeysTheName Group Title

thats fine (:

5. SmokeysTheName Group Title

@hero can you help with this?

6. Hero Group Title

Pretty easy stuff @SmokeysTheName

7. SmokeysTheName Group Title

its been forever since ive done this and i can't remember /: so can you help him?

8. Hero Group Title

Hint: m1 x m2 = -1

9. RealityWillSlapYou Group Title

Umm.... I not really sure.. :|

10. Hero Group Title

m1 = -3 So m2 has to be a number such that when multiplied by m1, their product is -1.

11. RealityWillSlapYou Group Title

-1?

12. RealityWillSlapYou Group Title

Then 1 x -1 = -1

13. RealityWillSlapYou Group Title

Right?

14. Hero Group Title

m1 = -3 Multiply -3 by something to get -1

15. RealityWillSlapYou Group Title

I have no clue..... :|

16. SmokeysTheName Group Title

is that even possible @hero?

17. Hero Group Title

-3 x 1/3 = -1

18. Hero Group Title

Yes, it is possible.

19. Hero Group Title

So that's basically the slope of the second equation.

20. SmokeysTheName Group Title

oh yeah xD lol i dont like fractions so i didnt think of it. my bad okay ill stay out of this..

21. RealityWillSlapYou Group Title

Oh, why is math so hard for me to understand?!

22. Hero Group Title

So now, you have the slope and the point. Use the point slope formula to figure out the value of b.

23. RealityWillSlapYou Group Title

Y U NO WORK FOR ME MATH?! (ノಠ益ಠ)ノ

24. phi Group Title

sometimes it helps to watch these videos http://www.khanacademy.org/math/trigonometry/graphs/parallel_perpendicular/v/equations-of-parallel-and-perpendicular-lines

25. SmokeysTheName Group Title

phi is right, khan acad vids are great to watch

26. RealityWillSlapYou Group Title

@phi, in the video he was using two points and my question only has one point so how can I solve it the same way?

27. phi Group Title

at the very end he does a problem like yours.

28. RealityWillSlapYou Group Title

Oh, my video sever crashed after the second equation.

29. phi Group Title

but this video assumes you know about slopes and equations of lines (he has videos on all of that) for you problem, you should know that when you see y = mx +b m is the slope. the number multiplying the x is the slope

30. RealityWillSlapYou Group Title

I will start it back up again, but it will take 2 min.

31. RealityWillSlapYou Group Title

I tried to solve it (I think I did it wrong) and is it C?

32. phi Group Title

for you problem, you should know that when you see y = mx +b m is the slope. the number multiplying the x is the slope so what is the slope of your line y = −3x − 1 ?

33. RealityWillSlapYou Group Title

-3?

34. phi Group Title

do you see a number in front of the x ?

35. RealityWillSlapYou Group Title

36. phi Group Title

yes, -3 is the slope (that is why people came up with this kind of equation, you can read off the slope easily)

37. phi Group Title

from the video, you learned that parallel lines have what kind of slope ?

38. RealityWillSlapYou Group Title

The same slope

39. phi Group Title

look at your 4 choices. which choices have the correct slope of -3 for the parallel line ?

40. RealityWillSlapYou Group Title

Well it's A or B....... I think it's B

41. phi Group Title

no need to guess. now for the perpendicular line. Its slope is the negative inverse (or negative reciprocal) that means "flip" the slope and multiply by -1. For example if you had slope =2 $\frac{2}{1} ->- \frac{1}{2}$ can you do that for -3 ?

42. RealityWillSlapYou Group Title

$\frac{ 3 }{ 1 }?$

43. RealityWillSlapYou Group Title

Or$\frac{ 1 }{ 3 }?$

44. phi Group Title

3/1 is 3 start with -3 or -3/1 minus it : - -3/1 is +3/1 now flip it : 1/3 you know you did it right if it is the opposite sign of -3, and it's "upside down"

45. RealityWillSlapYou Group Title

Okay

46. phi Group Title

the slope of the perpendicular is 1/3 look at choices A or B. can we rule out either choice because it does not have 1/3 for the slope of the perpendicular line ?

47. RealityWillSlapYou Group Title

We can rule out A, right?

48. phi Group Title

for choice A, what is the number in front of the x for the perpendicular line ?

49. RealityWillSlapYou Group Title

-3

50. phi Group Title

that is the parallel line

51. phi Group Title

A. parallel: y = −3x + 6 perpendicular: y = (1/3)x + 2(2/3)

52. RealityWillSlapYou Group Title

So we rule out B?

53. phi Group Title

B. parallel: y = −3x + 10 perpendicular: y = (1/3)x what is the slope for the perpendicular line ?

54. RealityWillSlapYou Group Title

1/3

55. phi Group Title

so both A and B pass. we have to use the last bit of info pass through the point (3, 1) that says that when x=3 y must = 1 test choice B, perpendicular (because it looks the easiest) y = (1/3)x replace x with 3 and do the arithmetic what do you get ?

56. phi Group Title

replace x with 3 that means wherever you see an x, put a 3 in its place.

57. RealityWillSlapYou Group Title

okay give me a min.

58. RealityWillSlapYou Group Title

y = (1/3)3

59. RealityWillSlapYou Group Title

??

60. phi Group Title

yes, $y= \frac{1}{3} \cdot 3$ you can think of the 3 as 3/1 or $y= \frac{1}{3} \cdot \frac{3}{1}$ when you multiply fractions, multiply top times top and bottom times bottom you get $y= \frac{3}{3}$ can you simplify this ?

61. RealityWillSlapYou Group Title

y = 1

62. phi Group Title

so (3,1) is on this line. this is the choice

63. phi Group Title

if we put x=3 in choice A, we will not get y=1 btw, we should check the parallel line can you do that ? parallel: y = −3x + 10 what do you get if you replace x with 3

64. RealityWillSlapYou Group Title

-9

65. phi Group Title

66. RealityWillSlapYou Group Title

1

67. phi Group Title

y = −3x + 10 if this does not give you y=1 when x=3 then it is not the line. But it does give y=1 so choice B. Does any of this make sense ?

68. RealityWillSlapYou Group Title

Yeah....

69. RealityWillSlapYou Group Title

How many more questions can you help me with?

70. phi Group Title

how many do you have ?

71. RealityWillSlapYou Group Title

Three, but I'm really bad at math.

72. phi Group Title

did you post them yet ?

73. RealityWillSlapYou Group Title

I posted one of them in algebra