Question

What is the equation of the line that passes through the points (-1, 3) and (1, 11)?

PLEASE HELP !!!!!!!!!!!

Answer 1

@harsimran_hs4 yes i do know the slope intercept form is y=mx+c

but how would you plug it in and get 2 equations?

Answer 2

3 = m(-1) + c
11 = m(1) + c
now can you solve for m and c?

Answer 3

First you don't know the slope so you need to find the slop m=y2-y1/x2-x1

Answer 4

okay i did that and got 8/2 .. correct? @begzat

Answer 5

okay so next step y-y1=m*(x-x1) take one of the points and plug in to the equation

Answer 6

okay i did that and got 8/2 .. correct? Yes, but 8/2 can be simplified to 4
that means the slope is 4.

you now know y = 4x + b
you need to find b

Answer 7

how can i find b? @phi

Answer 8

there are 2 ways (at least). one way is use begzat's formula

another is replace y and x with numbers that you know are on the line.
you know (-1, 3) is on the line. That means x= -1 and y=3
put those numbers in
y= 4x + b

3= 4*-1+b
can you solve for b?

Answer 9

the first step is simplify 4* -1 is -4, so you have
3= -4 + b

Answer 10

can you finish?

Answer 11

sadly .. no i can't. @phi

Answer 12

Ok, you might want to look at
http://www.khanacademy.org/math/algebra/solving-linear-equations-and-inequalities/equations_beginner/v/simple-equations
and the other videos. It is worth learning this or you will suffer in math class. Get some popcorn and watch them.

Answer 13

but if he do with the formula that i told maybe will be much easy i think :)

Answer 14

meanwhile
3= -4 + b

you want the b by itself. To make that happen , we add +4 to both sides of the equation
3+4= -4+4+b
the -4+4 =0 and the 3+4=7
7 = 0+b
0+b is just b
we get
7= b or b=7

now you can write down the equation of the line

Answer 15

Thank you so much and i will check out the videos. 4x - y = -7 correct? @phi

Answer 16

we know m=4 and b=7, so
y= 4x+7
if we move the y to the other side (add -y to both sides)
y -y = 4x -y +7
or
0 = 4x -y +7
now move the 7 to the other side, (add -7 to both sides)

-7 = 4x -y + 7 -7
or
-7 =4x -y
we can write that the other way around:
4x-y = -7

(notice you need to use algebra to swap the terms around)

Answer 17

Thank you soo much! i'm studying for a really big test tomorrow lol thank you for the video link @phi