The 'Help me with Calculus' Thread

**Vantage** · 08-09-2013, 05:56 PM

My Calc 1 final is next Thursday and I'm really doing pretty awful as a few things are just not clicking with me. So I was hoping some of you smart math wizards might take pity on me and throw me a bone. I go and see my GSI pretty much every time he has office hours and it has helped tremendously, but I feel I'm still way behind the curve...

To start it off I guess, one thing I'm pretty terrible at is interpretation(amoung many others)...(Note: all problems are example/class problems and not homework or anything so you wouldn't be helping me 'cheat' if someone felt it was a moral conflict somehow.) It's easier to just post pictures of the problems, rather than trying to find all the special characters so:

Thanks in advance to any and all who don't mind giving me a hand.

**Alex3000gt** · 08-10-2013, 12:57 AM

I can do this, but my eyes are bleary and it is 1AM. Classic initial condition and boundary condition problem.

Will post back tomorrow, err, today.

**futurevr4man** · 08-10-2013, 01:05 AM

i am no math genius, but i am a mechanical engineer and have taken all the math you can take... with that being said, i have NEVER seen a problem like this hahaha. this crap is so useless, it kills me sometimes.

anyhow, do you have the answers? i assume its looking for C(t)? i have never heard of 'interpretation' before, so im just a little lost as to what exactly the question is asking. if i could see an example i could make sense of it, and be fine from there (may wanna upload a pic of an example?).

using the decay model i got C(t) = 3385e^(-.4t) but i do not think that is correct... i also dont think you should have to rely on a model for the answer... but i have seen crazier crap happen.

so for TL;DR:

- do you have answers?
- do you have example problems worked out you could snap a photo of?
- are we solving for C(t)? if not, what do they mean by 'interpret'?

i swear i can do math, but this is beyond me for some reason. maybe cause its too late...

**Vantage** · 08-10-2013, 01:18 AM

Originally Posted by Alex3000gt

I can do this, but my eyes are bleary and it is 1AM. Classic initial condition and boundary condition problem.

Will post back tomorrow, err, today.

Thanks you good sir, I'm looking forward to it!

vr4man, I hear ya. Some of the problems are just..yea..pretty out there but it is what it is I guess. By 'Interpret' they just mean to put it into words. eg Describe in words what C'(10) = -0.4 in the context of the problem. I think I'm getting better at it but..meh, it's not something that's easy to check answers for as you can imagine, but it's all over the exams unfortunately.

**futurevr4man** · 08-10-2013, 01:58 AM

oh, so you mean like

"c'(10) = -0.4 means that at 10 minutes the temperature would be dropping at a rate of .4 degrees/minute"?

i could do all of those, no problem

. if my understanding is correct, these questions are actually fairly helpful. helps you understand theory and have a better general understanding of what mathematical language is saying.

**Vantage** · 08-10-2013, 10:59 AM

Kind of, and what you said is usually how I 'interpret' them. And I'm always wrong. lol I do certainly agree that being able to put these in words would be very helpful/useful but I seem to just keep missing the mark (and it seems to be such an easy concept

)

For example, the first interpretation problem we did in class was so far out of the realm of reason and the explanation I got was "its just a bad example."
------------------------
Problem 1
The cost C in thousand dollars of building a house A square feet in area is given by C = f(A).
(a) Interpret f'(100) = 200.

Answer: f(101) is approximately 200,000 dollars more than f(100) costs of building a house of 100 sqft.

(b) If a 100 sqft house costs 30000, estimate the cost of building a house of 100.5 sqft.

Answer:
f'(100) = 200, so a 101 would = an additional 200, so half of that: 100.5 would require an additional 100.

So, a 100.5 sqft house costs approximately $130,000.
------------------------

I certainly do agree that's just a crappy problem in terms of making real world sense. An apparently I'm never suppose to use the word "rate," unless he meant only when interpreting integrals and not derivatives.

I'm not to bad at interpreting first derivatives, it's when they start shuffling it up with the inverses and second derivatives that I start to lose it.

**futurevr4man** · 08-10-2013, 12:15 PM

hmm. i understand now but im not sure i could help you to understand it any better. it is certainly silly, i can tell you that. is this the only thing youre struggling with in this class?

**Vantage** · 08-10-2013, 12:49 PM

Originally Posted by futurevr4man

hmm. i understand now but im not sure i could help you to understand it any better. it is certainly silly, i can tell you that. is this the only thing youre struggling with in this class?

Oh goodness no. I think my biggest problem with these interpretations is just over thinking it. I was just hoping someone could put it in more layman's terms somehow as my instructor is a grad student from China, and while a nice guy, can have difficulty explaining the reason for some things. I'm hit or miss taking some of the more complicated derivatives but I'm pretty much going to spend the rest of the weekend doing them and practice exams. And since everything pretty much seems to revolve around the manipulation of the derivative, hopefully I'll be on the up and up. I'm sure I'll have some more questions to post if you guys don't mind.