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Mathematics 8 Online
OpenStudy (anonymous):

screenshots attached!

OpenStudy (anonymous):

jimthompson5910 (jim_thompson5910):

Average rate of change on the interval [a,b] for f(x) \[\Large m = \frac{f(b)-f(a)}{b-a}\] m is the average rate of change

OpenStudy (anonymous):

the part where it says solve on this interval confuses me, i don't know how to get that

OpenStudy (anonymous):

thank your for taking the time to help me, greatly appreciate it

jimthompson5910 (jim_thompson5910):

we have f(t) = 4t^2 - 1

jimthompson5910 (jim_thompson5910):

what is f(5) ?

OpenStudy (anonymous):

the domain?

jimthompson5910 (jim_thompson5910):

no what happens when you plug t = 5 into f(t) = 4t^2 - 1

jimthompson5910 (jim_thompson5910):

f(t) = 4t^2 - 1 f(5) = 4(5)^2 - 1 ... replace every 't' with 5 f(5) = ???

OpenStudy (anonymous):

oh 99!!!!

jimthompson5910 (jim_thompson5910):

what is f(5.1) equal to

OpenStudy (anonymous):

5.1 or 5? dont i plug in 5

jimthompson5910 (jim_thompson5910):

when we say f(5.1) and when f(t) = 4t^2 - 1, we are replacing every t with 5.1

jimthompson5910 (jim_thompson5910):

f(3) means replace every t with 3 etc etc

OpenStudy (anonymous):

4(5.1)^2-1=103.04

jimthompson5910 (jim_thompson5910):

so we know this f(5) = 99 f(5.1) = 103.04

jimthompson5910 (jim_thompson5910):

we now plug that into the formula \[\Large m = \frac{f(b)-f(a)}{b-a}\] in this case a = 5 b = 5.1

jimthompson5910 (jim_thompson5910):

so... \[\Large m = \frac{f(b)-f(a)}{b-a}\] \[\Large m = \frac{f(5)-f(5.1)}{5-5.1}\] \[\Large m = \frac{99-103.04}{5-5.1}\] \[\Large m = \frac{-4.04}{-0.1}\] \[\Large m = 40.4\]

OpenStudy (anonymous):

perfect!!! thank you!!!!!

jimthompson5910 (jim_thompson5910):

oh sry I have a = 5.1 and b = 5 but it really doesn't matter (since you can swap a and b easily)

jimthompson5910 (jim_thompson5910):

anyways, the average rate of change is 40.4 this represents the slope of the line through (5, 99) and (5.1, 103.04)

OpenStudy (anonymous):

so my final 3 answers? i don't get how the web assign system wants it

jimthompson5910 (jim_thompson5910):

so that's why it looks very similar to the slope formula (because in a way, it is the slope formula)

jimthompson5910 (jim_thompson5910):

do you know how to find the derivative?

OpenStudy (anonymous):

oh genius!

OpenStudy (anonymous):

no! i was having a lot of trouble yesterday with that

jimthompson5910 (jim_thompson5910):

have you learned about calculus topics yet? like limits and derivatives

OpenStudy (anonymous):

i am taking this class online and I've tried, but its harder online

OpenStudy (anonymous):

technically according to my homework i should know them already...

jimthompson5910 (jim_thompson5910):

so the lesson plan isn't that nailed down

OpenStudy (anonymous):

not at all!!

jimthompson5910 (jim_thompson5910):

ok well when you get free time, I recommend you read over these notes http://tutorial.math.lamar.edu/Classes/CalcI/CalcI.aspx go through it and see what makes sense and what doesn't. Then you can come back here and ask questions on stuff you don't get

jimthompson5910 (jim_thompson5910):

anyways, you'll use derivatives to derive f(t) to get f ' (t) this will give you a function that allows you to find the instantaneous rate of change at any point

OpenStudy (anonymous):

thank you, the link has been saved, and will look at it after i finish these problems!

OpenStudy (anonymous):

okay

jimthompson5910 (jim_thompson5910):

to derive, we will use the power rule http://tutorial.math.lamar.edu/Classes/CalcI/DiffFormulas.aspx http://www.mathsisfun.com/calculus/derivatives-rules.html which is if f(x) = x^n then f ' (x) = n*x^(n-1)

jimthompson5910 (jim_thompson5910):

and we'll also use the constant coefficient rule

jimthompson5910 (jim_thompson5910):

so f(t) = 4t^2 - 1 d/dt [f(t]) = d/dt[4t^2 - 1] f ' (t) = 2*4t^(2-1) f ' (t) = 8t

OpenStudy (anonymous):

im familiar with the power rule, i just always apply it at worng times!

OpenStudy (anonymous):

okay.

jimthompson5910 (jim_thompson5910):

what is f ' (5) equal to?

OpenStudy (anonymous):

thank you for all the links!

OpenStudy (anonymous):

99?

jimthompson5910 (jim_thompson5910):

f ' (t) = 8t f ' (5) = 8*5 f ' (5) = 40

jimthompson5910 (jim_thompson5910):

so the instantaneous rate of change at t = 5 is 40

jimthompson5910 (jim_thompson5910):

notice how it's pretty close to that average rate of change we got before, which was 40.4

OpenStudy (anonymous):

yes!!!!! i see it clearly, but without help i won't figure it out

jimthompson5910 (jim_thompson5910):

you will once you practice more and read over notes like what I posted

OpenStudy (anonymous):

thank you! i will!

jimthompson5910 (jim_thompson5910):

you're welcome

OpenStudy (anonymous):

so then my answers are 40 at t5 and 40.1 at t5.1

jimthompson5910 (jim_thompson5910):

not 40.1

OpenStudy (anonymous):

40.1 goes on the top

jimthompson5910 (jim_thompson5910):

f ' (t) = 8t f ' (5.1) = 8*5.1 f ' (5.1) = 40.8

jimthompson5910 (jim_thompson5910):

the instantaneous rate of change at t = 5.1 is 40.8

OpenStudy (anonymous):

and the top answer? the first empty box?

jimthompson5910 (jim_thompson5910):

that was the avg rate of change, aka the slope of the line through (5, 99) and (5.1, 103.04)

jimthompson5910 (jim_thompson5910):

this is what I get

OpenStudy (anonymous):

i thought that one is 40.4?

jimthompson5910 (jim_thompson5910):

the last one, you'll do V(s) = s^3 V ' (s) = 3s^2 V ' (19) = 3*19^2 V ' (19) = 1083

OpenStudy (anonymous):

this is what i have

jimthompson5910 (jim_thompson5910):

correct so far

OpenStudy (anonymous):

of course because you gave them to me! lol

OpenStudy (anonymous):

thank you for the second question:)

jimthompson5910 (jim_thompson5910):

lol well hopefully it's clicking that you could find similar problems in the future

jimthompson5910 (jim_thompson5910):

np

OpenStudy (anonymous):

I'm going to practice different versions after i get this one correctly

jimthompson5910 (jim_thompson5910):

good idea

OpenStudy (anonymous):

OpenStudy (anonymous):

i think I'm done?

OpenStudy (anonymous):

no its .8?

OpenStudy (anonymous):

the only one left is we just subtract 40.8-40

jimthompson5910 (jim_thompson5910):

see this

jimthompson5910 (jim_thompson5910):

\[\Large m = \frac{f(b)-f(a)}{b-a}\] \[\Large m = \frac{f(5)-f(5.1)}{5-5.1}\] \[\Large m = \frac{99-103.04}{5-5.1}\] \[\Large m = \frac{-4.04}{-0.1}\] \[\Large m = 40.4\]

OpenStudy (anonymous):

oh gosh i was so wrong!!!

OpenStudy (anonymous):

thank you it was all right!

OpenStudy (anonymous):

do u want to help me with my last one? I'll really try to do it?

jimthompson5910 (jim_thompson5910):

ok go ahead and post it

OpenStudy (anonymous):

OpenStudy (anonymous):

:) Thank you

jimthompson5910 (jim_thompson5910):

we'll use the idea that |dw:1411089469334:dw|

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