Mathematics
OpenStudy (anonymous):

Find the equation of the line in the graph and mathematically model the scenario using function notation where cost is a function of number of minutes.

OpenStudy (anonymous):

OpenStudy (anonymous):

OpenStudy (anonymous):

I don't know how to find the function.

OpenStudy (anonymous):

@ganeshie8

OpenStudy (anonymous):

Right back at you, hypocrite.

OpenStudy (phi):

the function looks like a line to me... I would find the slope: change in y divided by change in x then find the y -intercept (what is y when x is 0) then write f(x) = m x + b where m is the slope that you found, and b is the y-intercept you found

OpenStudy (anonymous):

What he said ^ | | |

OpenStudy (anonymous):

@phi I don't understand

OpenStudy (phi):

which part ? do you agree it looks like a line ?

OpenStudy (anonymous):

Yes but the line only seems to intersect the y line

OpenStudy (phi):
OpenStudy (anonymous):

Okay

OpenStudy (anonymous):

Ohhh I get it.

OpenStudy (phi):

what do you get for the slope ?

OpenStudy (anonymous):

I finished the video and I see what he did, but I still need to figure out my problem. This will take a minute or two . . .

OpenStudy (anonymous):

I got 1/4

OpenStudy (phi):

right idea... but you have to use the numbers they gave you. 4 "boxes" on the x-axis is 400 steps 1 "box" on the y-axis is 20

OpenStudy (anonymous):

Oh so I have 400/80??

OpenStudy (phi):

OpenStudy (phi):

can you see that y starts at 20 and goes up to 40 ? what is the change in y ? can yo see that x starts at 0 and goes up to 400 ? what is the change in x?

OpenStudy (anonymous):

Yes so y changes 20, and x changes 400.

OpenStudy (anonymous):

So in 400 minutes the cost of the phone is \$40

OpenStudy (phi):

yes, and slope= change in y over change in x = 20/400 you can simplify that to 2/40 or 1/20 the slope is 1/20 the y-intercept is the y value when x is 0. can you read that number off the graph ?

OpenStudy (anonymous):

So the y-intercept is 20?

OpenStudy (anonymous):

But the question wants me to create an equation for the graph

OpenStudy (phi):

yes, now use m= 1/20 and b= 20 in f(x) = m x + b this will be the equation of the line

OpenStudy (anonymous):

So the equation is f(x) = 1/20x + 20 ??

OpenStudy (anonymous):

But the question wants me to create an equation for the graph

OpenStudy (anonymous):

So the y-intercept is 20?

OpenStudy (phi):

So the equation is f(x) = 1/20x + 20 ?? yes but I would write it f(x) = (1/20) x + 20 just to make it clear it is 1/20 times x and not 1 divided by (20x) as a test, if we try x=200 we get f(200)= (1/20) * 200 + 20 1/20 times 200 is 10 f(200) = 10+20 = 30 if we look at the graph, we see the y value (or f(x) value) when x=200 is 30 it works!
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