<p>Help me find the derivative of this: f(x) = 360/x + 40x +90</p>
<p>I know how to find derivatives and i know the answer is supposed to be this: -360x^-2 + 40 </p>
<p>Im getting lost somewhere in the steps, can someone break it down for me? Appreciate it alot! </p>
<p>(Calc stuff >.<) this is the problem btw (i found the answer on google to make sure how i was progressing so far, but i cant seem to get the derivative -_-)</p>
<p>A tank with a rectangular base and rectangular sides is to be open at the top. It is to be constructed so that its width is 4 meters and its volume is 36 cubic meters. If building the tank costs $10 per square meter for the base and $5 per square meter for the sides, what is the cost of the least expensive tank?</p>
<p>Here’s the answer: rewrite 360/x as 360x^(-1), and use the power rule.</p>
<p>f(x) = 360x^(-1) + 40x + 90.</p>
<p>Find the derivative of each term with the power rule. Multiply the coefficient by the exponent, and then decrease the exponent by 1. (NOTE: this will make the derivative of any constant 0. Because k = kx^0, the derivative of k will be (0)k^(-1), which equals 0.)</p>
<p>f '(x) = (-1)360x^(-2) + (1)40x^0 + (0)90x^(-1) = -360x^(-2) + 40 </p>
<p>Are you just beginning to learn calculus? If so, then I understand why you might ask. </p>
<p>But honestly, if not, I’m stunned that you couldn’t take this derivative. It’s quite basic. It makes me wonder whether you know how to take a derivative as well as you believe you do. </p>
<p>I say this as a math teacher, and not as just some guy on the Internet who’s trying to pick a fight with you.</p>
<p>CORRECTION:</p>
<p>
</p>
<p>This sentence should read: Because k = kx^0, the derivative of k will be (0)kx^(-1), which equals 0.</p>
<p>Yes, thank you! I’m going into ap Calc AB in September ( Senior Year ) it is the highest math my school offers. Totally new to calc.</p>
<p>Well, that makes sense then!</p>
<p>I was concerned, but if you’re about to start taking calculus…</p>
<p>Sent from my DROIDX using CC App</p>
<p>ah!!! thank you! I understand that now but one more thing you didnt answer, could you possibly show your steps in finding the derivative from the formula f’(x) = f(x+h) - f(x)/h</p>
<p>I got to some strange answer and got kinda sorta stuck.</p>
<p>With a keyboard?</p>
<p>I hate to seem ungenerous, but no. Sorry.</p>
<p>lol its okay, i figured it out. i forgot to reply that. thanks though.</p>
<p>^ For the record, if you were able to work out the derivative for that expression starting from the definition of a derivative without using the rule for power functions, on your own, BEFORE you have taken the class…you should be proud! It’s an ugly mess to work through and no one will make you do it that way after you learn the formulas. Nice job.</p>
<p>haha thank you. I start class in 2 and a half weeks and i got two giant summer packets labeled “review before calculus”…turns out i needed to self-teach some basic calc haha</p>
<p>PCKeller, good point. I feel kind of sheepish that I neglected to say it myself.</p>