Question

How would I do this?


What is an equation for the line that passes through points (-1, -4) and (1, 4)? Write the equation in slope-intercept form.

Answer 1

do you know how to find the slope between two points?

Answer 2

Yes, I know how to do that. So, it would be like this.
m = y2 - y1 over x2 - x1
m = 4 - (-4) over 1 - (-1)

Am I doing it correctly?

Answer 3

This would make 8 over 2. Therefore, forming 4/1 which turns into 4.
@phi: Did I do it right?

Answer 4

However, they want it in slope-intercept form...

Answer 5

yes you found the slope.
slope intercept form is
y= mx + b
where m is the slope and b is the y-intercept (where the line crosses the y-axis)
with m=4 you have
y= 4x+b

you have to find b to finish the problem
one way is replace x and y with numbers that are on the line
for example (1, 4) is on the line. (1,4) means x=1 and y=4
replace x and y in your equation
4= 4*1+b
can you find b?

Answer 6

Okay, hold on please.

Answer 7

Why do you have the * symbol after the 4? Would we just put the 1 in parenthesis after it instead?

Answer 8

B is the y-intercept so that would make it -4 I believe.

Answer 9

* means multiply in lots of computer programming languages
you could write 4*1 as 4(1). or with a dot \(4\cdot 1\)

Answer 10

for example (1, 4) is on the line. (1,4) means x=1 and y=4
replace x and y in your equation
4= 4*1+b

or
4= 4+b

b=4 would make this 4= 4+4 or 4=8 which is not correct
to solve for b, add -4 to both sides
4-4= 4+b-4
and simplify

Answer 11

b= -4 is equally bad

Answer 12

I'm here just to let you know. I had to do something real quick. I'm going to read what you posted now.

Answer 13

Okay, I understand. They just want me to state the equation for the line in slope-intercept form so it would be this: 4 = 4(1) + -4 Correct?

Answer 14

you are missing an idea ?

you are asked to find the equation of a line in slope intercept form
y= mx +b

so the answer will be in that form. notice that 4 = 4(1) + -4 does not have an x or y, so that can't be right.

m is the slope. you found the slope. it is m=4
so you know some of the equation

y= 4x +b

now you need to find b and you will be done.

Answer 15

Okay, so we just leave the y and x in its variable form like you did, and make sure that we state the values of m and b?

Answer 16

yes, now you must find b

you use algebra. to find b, use a point you know is on the line.
(1,4) is on the line (they told you this)

so
4= 4(1) +b must be true
4=4+b
what b makes this an equality?

Answer 17

0?

Answer 18

yes. b=0

if you use algebra
4+b= 4
you would write down -4 on both sides of the =
4+b-4= 4 - 4
on the right side 4-4 is 0
4+b-4= 0
on the left, you can change the order when adding: b+4-4
and b+ (4-4) is b+0 or just b
we get
b=0

so finally, we have your equation
y= mx+b with m=4 and b=0
y= 4x +0
but nobody writes + 0, so the answer is

y= 4x

Answer 19

Okay, thanks for your help! :)