Processing math: 100%
 
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hello guys it had been long since last login of mine.

derivative problem again......

Find f'(x) for f(x)=3xlnx(lnx)(x31)2xsinxcotx

Best Answer 

 #3
avatar+9675 
+5

That used me 75 minutes and I didn't use any software......

 Sep 4, 2016
 #1
avatar+33657 
+5

Too many steps to include here, so here's the result given by Mathcad:

 

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 Sep 4, 2016
 #2
avatar+9675 
+5

That's really a complicated one......

I will give it a go.

f(x)=3xlnx(lnx)(x31)2xsinxcotx=(32)x(lnx(lnx)(x31)cosx)

=(32)x(lnxcosx)((lnx)(x31))

There we seperate it into 3 parts!!

Part 1 = (3/2)^x

Part 2 = (ln x)/(cos x)

Part 3 = sqrt((ln x)(x^(sqrt 3 - 1)))

Next we will find the derivative of (3/2)^x using implicit differentiation......

y=(32)xlny=xln321ydydx=ln32dydx=yln32=(32)x(ln32)

Then we find the derivative of ln x/ cos x......

(lnxcosx)=(1x)(cosx)(sinx)(lnx)cos2x=cosxx+sinxlnxcos2x=1xcosx+tanxlnxcosx=1+xtanxlnxxcosx

Then we came to the most complicated part: derivative of sqrt((ln x)(x^(sqrt 3 - 1)))

((lnx)(x31))y=uu=(lnx)(x31)y=(x32)+((31)(lnx)(x32))2lnx(x31)

Next we apply the product rule to Part 1 and Part 2 and call it Part 1,2

(Part 1 times Part 2)' 

= Part 1 ' Part 2 + Part 2 ' Part 1

((32)xln32)(lnxcosx)+(1+xtanxlnxxcosx)(32)x

(3xlnxln33xlnxln22xcosx)+(3x+3xxtanxlnx2xxcosx)

=3x(xlnxln3xlnxln2+1+xtanxlnx)2xxcosx

I will name this fraction y.

Then we find the derivative of Part1,2:

3xlnx(xlnxln3xlnxln2+1+xtanxlnx)+3x(lnxln3+ln3lnxln2ln2+tanxlnx+xsec2xlnx+tanx)22xx2cos2xOops it's too long :( I will name this looooooonnnnnggggg fraction z then)

Then we use product rule for Part1,2 and Part 3:

f'(x)= y(x32+(31)(lnx)(x32)2lnx(x31))+z(lnx(x31))

 Sep 4, 2016
edited by MaxWong  Sep 4, 2016
 #3
avatar+9675 
+5
Best Answer

That used me 75 minutes and I didn't use any software......

MaxWong  Sep 4, 2016
 #4
avatar+9675 
+5

Tips: To see all of that loooooonng fraction:

Right click any LaTeX -> Move the cursor to 'Math Settings' -> Click 'Scale all Math' -> Change it to 30% instead of 100% 

This would make everything smaller but you would be able to see all of that fraction z!!

MaxWong  Sep 4, 2016

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