What is an equation for the line that passes through points (–1, –4) and (1, 4)? Write the equation in slope-intercept form. (2 points)

- anonymous

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- anonymous

y = mx + b
m=(y2-y1)/(x2-x1)

- anonymous

@lolly wanna try

- anonymous

no..but i will..:)

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- anonymous

(1,-4), m = -4
y = mx + b
Sub to find b
-4 = -4*1 + b
b = 0
-------
y = -4x
m = -4 means slope = -4.
slope-intercept form of equation of a straight line is y = mx + b.
m is the slope.
b is the y-intercept.
your equation starts of with the slope-intercept generic form of y = mx + b
replace m with -4 to get y = -4x + b
your line goes through the point (x,y) = (1,-4)
that means the x-coordinate is 1 and the y coordinate is -4.
to find the y-intercept, you replace y with -4 and x with 1 in the equation and solve for b.
your equation of y = -4x + b becomes:
-4 = (-4 * 1) + b

- anonymous

can you set up the equation? then ill solve:P

- anonymous

@swiftskier96 is that the answer http://www.algebra.com/algebra/homework/Graphs/Graphs.faq.question.233716.html hahaha

- anonymous

(x1,y1) = (–1, –4)
(x2,y2) = (1, 4)

- anonymous

soo y=mx=b? isnt that for finding slope?

- anonymous

yes but you need to find m 1st
\[y=\frac{ y2-y1 }{ x2-x1 }\]

- anonymous

meant m =

- anonymous

ook ill try it..hold on..:)

- anonymous

m=-6

- anonymous

now what?

- anonymous

show me how?

- anonymous

m is wrong :D

- anonymous

really?

- anonymous

m= 1-4/-1--4.
m=-3/3
m=-6

- anonymous

(x1,y1) = (–1, –4)
(x2,y2) = (1, 4)
x1 = -1
y1 = -4
x2 = 1
y2 = 4

- anonymous

hi lolly :P

- anonymous

right..thats what i did..,.i think..?

- anonymous

hi..:)

- anonymous

(y-y1)/(y2-y1)=(x-x1)/(x2-x1)

- anonymous

@surdawi how did i do it rong?

- anonymous

(4- - 4)/(1- -1)= 8/2=4

- anonymous

so m is 4?

- anonymous

what you did (x2-y2)/(x1-y1)

- anonymous

well i thought it was -6..but its not..?

- anonymous

m = 4
now you choose wither point and solve for b
y = 4x + b

- anonymous

k hold on ill try again..:)

- anonymous

\[m=\frac{ y2-y1 }{ x2-x1 }=\frac{ 4- -4 }{ 1- -1 }=\frac{ 8 }{ 2 }=\]

- anonymous

for slope
slope=(y2-y1)/(x2-x1)
it can be directly solve see the formula that i have given already

- anonymous

(y-y1)/(y2-y1)=(x-x1)/(x2-x1)

- anonymous

oooh!!! i got the x1and 2s switched up..ok i see..:)

- anonymous

|dw:1351797990809:dw|

- anonymous

the one with less numbers right?

- anonymous

there is no zeros for x or y this time so pick one and solve, it doesnt matter which one

- anonymous

which one would be easier?

- anonymous

either, same thing

- anonymous

k ill do the one with less numbers..:P

- anonymous

so 4=4x1=b? 4=b..but we already knew that..

- anonymous

both of them has same amount of numbers :p
4=4x1=b? !
why is there an equal to b

- anonymous

oooh! whoop..my bad..:)

- anonymous

so 4=4+4...

- anonymous

4=8? that dosent make sense...

- anonymous

4=4x1+ b
what is x1 = ?

- anonymous

-1

- anonymous

y1 =?

- anonymous

-1

- anonymous

000h!!!

- anonymous

no it dosent..:)

- anonymous

-4

- anonymous

it should be one of the pairs either (1,4) or (-1,-4)
-4 = 4*(-1) + b

- anonymous

-4=4x-1=4?

- anonymous

4*-1=?

- anonymous

-4

- anonymous

-4 = -4 + b
how can you keep b on one side?

- anonymous

by adding 4 to b?

- anonymous

ok show me how?

- anonymous

-4=-4+b (then the 4 crosses out)
+4 +4

- anonymous

-4 +4 = -4 + 4 +b
0 = b
y = 4x + 0

- anonymous

where did the other set of -4=4 come from?

- anonymous

you have to add 4 to both sides

- anonymous

passes through points (–1, –4) and (1, 4)?

- anonymous

Anamaria what grade you in?

- anonymous

10.:)

- anonymous

you should know how to add :P

- anonymous

lol i do know how to add:)

- anonymous

-4=-4+b (then the 4 crosses out)
+4 +4
was this rong?

- anonymous

lol @surdawi u sleeping?

- anonymous

i went to pray
|dw:1351801108941:dw|

- anonymous

lol were u praying that id understand how to do this? lol jk ook umm anyway i thought b=4?

- anonymous

lol muslims pray 5 times a day not only sundays :P
ok plug in b = 4 to check
y = 4*x + 4
(1, 4)
4 = 4*1 + 4
4 = 8? is that right

- anonymous

4 is not 8...? im so confused!!

- anonymous

thats would be the answer if b was 4
correct answer is
y = 4x + 0 = 4x
plug in and check
and where is my medal at??

- anonymous

do you want me to give you problem to do?

- anonymous

try solving this
What is an equation for the line that passes through points (2,5) and (6,7)? Write the equation in slope-intercept form. (you pay $10 hehe)

- anonymous

noo i dont want another problem im too stuck with this one..:)

- anonymous

tell what you dont understand
|dw:1351802673845:dw|

- anonymous

i dont really understand what you did..like at all... for the one on the right side...

- anonymous

ok (-1,-4)
now we need to substitute that into y =mx + b
y = -4
x = -1
m = 4
y = m* x + b
-4 = 4*(-1) + b
-4 = -4 + b
we now need to add a 4 to both sides
-4 = -4 + b
+4 +4
--------------
0 = 0 + b ===> b = 0

- anonymous

ok so b = 4 and 0?

- anonymous

no only 0
how do you get the 4?

- anonymous

what we did earlier..

- anonymous

we never got b = 4
we got m is 4

- anonymous

oooh!!!

- anonymous

i have to go to my Advance Engineering Math :( right now; which doesnt look like anything on here...try to figure it out; if you still have problems feel free to message me
the answer is
y = 4x

- anonymous

k thanks 4 ur help:)

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