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Mathematics 18 Online
Ballery1:

Need help to solve a quick silly question..

Ballery1:

|dw:1570058681055:dw|

Ballery1:

I know we use natural log...but i forgot how to apply the natural log derivative

Ballery1:

I need a hint plz

Hero:

Where did you learn that you're supposed to use natural log to find the derivative of this?

Ballery1:

I remember that since the base isn’t a variable, you apply the natural log to the base and then apply the chain rule... that’s as far as i can remember

Hero:

What you're supposed to do is let \(u = 2x + 1\). Then take the derivative of \(e^u\) with respect to \(u\) and take the derivative of \(2x + 1\) with respect to x using the chain rule. There's no natural log involved in this.

Ballery1:

K so the question is to find the relative maxima and relative minima.... and i was suppose to find the first derivative of that expression and do a first derivative test to see where the graph changes from positive to negative and vice versa..

Hero:

All you have to do is just apply the chain rule here. The only reason the derivative of \(e^x\) is \(e^x\) is because the \(x\) is treated as the "outside" function and the derivative of \(x\) is just 1. And then \(1 \cdot e^x\) is just \(e^x\). So with \(e^{2x+1}\) it's the same way. \(2x + 1\) is treated as the outside function and the derivative of \(2x + 1\) is just 2. So then multiply two by the inside function \(e^{2x+1}\)

Ballery1:

Bro...it’s not e^2x+1 ...

Hero:

I don't know why I saw the three as an e

Ballery1:

|dw:1570059875762:dw|

Hero:

I glanced at it too fast

Ballery1:

I even said...the base is an integer... lol

Hero:

I was already convinced it was e by the time you posted that

Ballery1:

Jajajajaja

Ballery1:

Shall we proceed to solve the question master? :)

Hero:

The derivative of \(a^x\) is \(a^x \ln(a)\)

Ballery1:

Wait, let me draw

Ballery1:

|dw:1570060107828:dw|

Ballery1:

|dw:1570060193040:dw|

Hero:

Hang on, \(e\) IS involved in this

Ballery1:

Yikes..

Hero:

Apparently, you're supposed to use the exponent rule \(a^b = e^{b \ln(a)}\) before applying the derivative

Ballery1:

Wat? I was gonna use the log laws for some reason....you know, bring the 2x+1 to the front thingy

Hero:

You're supposed to find the derivative of 2x + 1 when you do that

Hero:

The answer you have is already correct. Just remove the \(x\) from the \(2x\)

Ballery1:

Wait one second... let me draw

Ballery1:

|dw:1570060542750:dw| Like this?

Ballery1:

Sorry, that was a silly mistake.

Hero:

Correct

Ballery1:

So what rule/equation do i use to find the derivative??? Plz let me know to avoid confusion

Hero:

Showing it to you would probably confuse you

Hero:

I guarantee it's in Larson's Calculus

Ballery1:

Nope, it’s from my college textbook...

Ballery1:

Literally they threw in this random expression out of nowhere... while before that i solved like 11 functions that had nothing to do with this kinda question..

Hero:

I meant the derivative rule is in the Larson Calculus textbook.

Ballery1:

Can you tell me tho :/ i need to include in my notes so i know what rule to apply the next time i study math again...next year

Hero:

You could find it in the textbook faster than I could explain it

Hero:

It's not exactly a simple to explain rule

Ballery1:

Aww... then how will i be able to remember what to do the next time i study this course with an empty mind??

Hero:

"next time you study this course". There's gonna be a next time? Why would you do that do yourself?

Ballery1:

|dw:1570061084816:dw|

Ballery1:

After that, i can just apply the power rule and collect terms

Hero:

The DERIVATIVE of a^x is a ln(a)

Hero:

You can't just post a^x is a^x ln(a) without proper context

Hero:

SMH, I'm making mistakes trying to cover your mistakes

Hero:

That was frustrating to see

Ballery1:

Khekhekhekhe

Hero:

The derivative of a^x is a^xln(a)

Hero:

That only works if it's just \(x\) in the exponent though

Hero:

Let me see something though.

Ballery1:

K so the context is that whenever i see a base as an integer, i take the ln of the base, then apply power rule and rearrange the terms ...

Hero:

Okay, so I did a little research and there's an alternative way to find the derivative that gives an equivalent result. (Equivalent meaning the result will look different but the expressions are still identical)

Hero:

Here it is: To find the derivative of \(3^{2x+1}\) Let's say the expression is \(a^{bx + c}\) We re-write it as \(a^{bx} \cdot a^{c}\) Then \(a^c\) is a constant and we can apply the constant rule \((cf)' = cf'\) In other words \(\boxed{(a^{bx} \cdot a^c)' = a^c(a^{bx})' = a^c [a^{bx} \ln(a) \times b]}\)

Hero:

There's your rule

Ballery1:

I see ... will i be able to apply the first derivative test on that tho ? Cuz i need to find where the expression is a relative maxima or a relative minima

Hero:

Yes

Ballery1:

I see now... k thanks mate. Really appreciated your help :)

Ballery1:

Check your dm now lol

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