Here's the question you clicked on:
RealityWillSlapYou
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
@SmokeysTheName, Right here!
ohhh man, remember i said i couldn't help? but here @phi might be able to
Oh, oops! Sorry about that.... :)
@hero can you help with this?
Pretty easy stuff @SmokeysTheName
its been forever since ive done this and i can't remember /: so can you help him?
Umm.... I not really sure.. :|
m1 = -3 So m2 has to be a number such that when multiplied by m1, their product is -1.
Then 1 x -1 = -1
m1 = -3 Multiply -3 by something to get -1
I have no clue..... :|
is that even possible @hero?
So that's basically the slope of the second equation.
oh yeah xD lol i dont like fractions so i didnt think of it. my bad okay ill stay out of this..
Oh, why is math so hard for me to understand?!
So now, you have the slope and the point. Use the point slope formula to figure out the value of b.
Y U NO WORK FOR ME MATH?! (ノಠ益ಠ)ノ
sometimes it helps to watch these videos http://www.khanacademy.org/math/trigonometry/graphs/parallel_perpendicular/v/equations-of-parallel-and-perpendicular-lines
phi is right, khan acad vids are great to watch
@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?
at the very end he does a problem like yours.
Oh, my video sever crashed after the second equation.
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
I will start it back up again, but it will take 2 min.
I tried to solve it (I think I did it wrong) and is it C?
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 ?
do you see a number in front of the x ?
So is the answer B?
yes, -3 is the slope (that is why people came up with this kind of equation, you can read off the slope easily)
from the video, you learned that parallel lines have what kind of slope ?
The same slope
look at your 4 choices. which choices have the correct slope of -3 for the parallel line ?
Well it's A or B....... I think it's B
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 ?
\[\frac{ 3 }{ 1 }?\]
Or\[\frac{ 1 }{ 3 }?\]
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"
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 ?
We can rule out A, right?
for choice A, what is the number in front of the x for the perpendicular line ?
A. parallel: y = −3x + 6 perpendicular: y = (1/3)x + 2(2/3)
So we rule out B?
B. parallel: y = −3x + 10 perpendicular: y = (1/3)x what is the slope for the perpendicular line ?
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 ?
replace x with 3 that means wherever you see an x, put a 3 in its place.
okay give me a min.
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 ?
so (3,1) is on this line. this is the choice
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
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 ?
How many more questions can you help me with?
Three, but I'm really bad at math.
I posted one of them in algebra