Question

Write an equation of the line in point slope form, that passes through the two given points (-2, 15) and (9, -18)?
(Not sure how to do this... help?)

Answer 1

So do you know the equation for slope?

Answer 2

Yes y2 - y1 over x2 - x1

Answer 3

Right. So what do you get for slope?

Answer 4

Just a minute...

Answer 5

-33/11

Answer 6

Right, now simplify that.

Answer 7

-3

Answer 8

Good. So now we have the equation y=-3x+b. Good so far?

Answer 9

Yup

Answer 10

Great. Now we choose a point and plug it in. Take the first one. We have 15=-3(2)+b. Now solve for b. What do you get?

Answer 11

Correction: 15=-3(-2)+b. Left out a negative. Sorry.

Answer 12

No problem... Do I multiply -2 by -3 first or divide -3 from both sides?

Answer 13

Multiply.

Answer 14

You should then get 15=6+b, and then subtract 6.

Answer 15

Ok Thanks So it's 9 = b

Answer 16

Right. So our solution is y=-3x+6.

Answer 17

But it's in point slope form not slope intercept?

Answer 18

Oh, sorry. So then we want to write it in point slope. Can you do that?

Answer 19

I'm not sure how really.

Answer 20

It's just\[y - 15 = -3(x+2)\]That's it.

Answer 21

Ok thank you I get that!

Answer 22

Great. Glad to help. Thanks for the medal!

Answer 23

No problem, um I have another quick question.

Answer 24

Fire away.

Answer 25

So if we were using point slope form and we knew the slope was 3 and 2 points were (8, -8) how would we write that?

Answer 26

Would it be y - 8 = 3 (x + 8) ?

Answer 27

We would write \[y+8 = 3(x-8)\]You messed up your signs.

Answer 28

Oops

Answer 29

Thank you I meant to have it the other way around!

Answer 30

Right.