<p>Bah. I have five 1st and 2nd derivatives I must do. I think I did the one I knew how to do wrong. Is there anyone who I can PM for help? I don't know what I'm doing. :(</p>
<p>Just ask your questions on this thread..</p>
<p>I have a lot. But okay...</p>
<p>5e^3x cos(x). I'm not sure how to tackle the first part. I know the chain rule and all that jazz but i'm not so great with e's.</p>
<p>x^4 + (5x^3)/72 -(x^2)/8 - 2x + 7. I just need to know where to start, I have no idea. At first I thought I should use the quotient rule, but now I don't know </p>
<p>x/(x^2+1). I did this one, so I just want the answer to see if I did it right.</p>
<p>(3x-5)^4(4x+11)^5. This is just product rule right? And chain rule? Right?</p>
<p>The last one was easy so I omitted it.</p>
<p>Thanks for your help. PM me, e-mail me, IM me, or post it here thanks. Any help at all would be great</p>
<p>1) You need to use the product rule. Set u=5<em>e^3x and v=cos(x). The answer is -5</em>e^3x(sin(x)-3cos(x)).</p>
<p>2) Differentiate each of the components individually.</p>
<p>3) (-x^2+1) / (x^2+1)^2</p>
<p>4) Yes, use the product and chain rules.</p>
<p>Okay my questions are:</p>
<p>for #2, how do I differentiate when it's something/constant?</p>
<p>Thanks for your help! :D I actually get it now!</p>
<p>d/dx ((5x^3) / 72) = (1/72) * d/dx (5x^3) = 15/72<em>x^2 = 5/24</em>x^2</p>
<p>The constant can be factored out. And no problem.</p>
<p>Man I just realized how quick I forgot Calculus!</p>
<p>Okay I see. I'm still a little confused on #1. I don't understand where the sinx-3cosx comes in.</p>
<p>It's been a while. But if I remember correctly h'(x), for h(x) = f(x)/g(x) is (f'(x)g(x)-f(x)g'(x))/(g(x)^2).</p>
<p>Edit: Should have refreshed before posting :). My bad.</p>
<p>For 1, </p>
<p>f(x) = 5e^3x<em>cos(x);
f'(x) = u</em>v' + v*u' (according to the product rule)</p>
<p>Let's set u=5e^3x and v=cos(x). Then u'=5<em>(e^3x)</em>3, and v'=-sin(x). So u<em>v' + v</em>u' = (5e^3x)<em>(-sin(x)) + (cos(x))</em>(15e^3x) = (-5e^3x)*(sin(x)-3cos(x)) = f'(x).</p>
<p>Oh I see. I was just being silly. Thanks for all your help! It really did help me a lot! <em>yippee</em> :D</p>
<p>I'm sure this is really stupid and I just missed something but how is d/dx(5e^3x) = 5<em>(e^3x)</em>3</p>
<p>Chain rule for the three at the end...but don't you have to do the derivative of e^3x with the power rule too?</p>
<p>nope, the derivative of e^x is e^x. you can only use the power rule when a variable is raised to a constant. you can't you use the power rule if something is raised to a variable.</p>
<p>e^u = e^u times du/dx</p>
<p>I don't want to hijack your thread Celebrian but...
I have a Calculus quiz tomorrow and lately I have been failing them. I was really frustrated because last week we had a test that I studied all day tuesday for (like >8 hours!) and then ended up flunking it anyway, so it was a waste of a day! </p>
<p>So I was wondering if any of you have any tips to study for tests. I do all the practice problems at least once, sometimes twice and always get the right answer but I don't know how I do so horribly on the test? </p>
<p>The quiz is on Hyperbolic Functions, Related Rates, and linear approximations and differentials. Is there anything you guys do to practice for Calc quizzes?</p>
<p>Ha, which reminds me, just failed mine today.
Funny, I never fail, but the common cold, fatigue, and NSAIDs got me in the end.
Never take Tylenol two hours before a test. Brain was so scrunched up that I couldn't subtract 16 from 12 without writing it on the paper. </p>
<p>We don't get to use our calculators, do you?</p>
<p>hahahaha
i totally failed a test on derivatives today</p>
<p>(but even if i got a zero, my average would still be an 80 for the 9 weeks. i rejoiced!)</p>
<p>good luck with all of that
i'd help if i could</p>
<p>zpmqxonw, </p>
<p>Look at what you did wrong on the test, and learn from your mistakes. From this you should also be able to learn how to study better. (And don't ever study for eight hours in a row again. That's too much.)</p>
<p>we don't get to use calculators either, liliachencko</p>
<p>We used calculators on our 1st test for a page and for one question on our last question just because it used numbers to big to easily do in the good ol' head, but besides that nope. :)</p>