calculus: Find y', if y = x^3 / 3^x (I get x^3=y'=3x^2...)

Re: calculus Y PRIME

venialove said:
find y' if y = x^3/3^x
\(\displaystyle \begin{gathered} y = \frac{{x^3 }}{{3^x }} = \left( {x^3 } \right)\left( {3^{ - x} } \right) \hfill \\ y' = \left( {3x^2 } \right)\left( {3^{ - x} } \right) + \left( {x^3 } \right)\left[ { - 3^{ - x} \left( {\ln (3)} \right)} \right] \hfill \\ \end{gathered}\)
 
Re: calculus Y PRIME

Hello, venialove!

Sorry, I have no idea what you did . . .


\(\displaystyle \text{Find }y'\,\text{ if }\,y \:= \:\frac{x^3}{3^x}\)

\(\displaystyle \text{Quotient Rule: }\;y' \;=\;\frac{3^x\!\cdot\!3x^2 - x^3\!\cdot\!3^x\!\cdot\!\ln3}{(3^x)^2}\)

\(\displaystyle \text{Factor: }\;y' \;=\;\frac{3^x\!\cdot\!x^2\left(3 - x\ln3)}{(3x)^2}\)

\(\displaystyle \text{Reduce: }\;y' \;=\;\frac{x^2(3 - x\ln3)}{3^x}\)

 
Re: calculus Y PRIME

venialove said:
find y' if y = x^3/3^x


My work"
x^3= y'= 3x^2<<< what is this - 2 "=" signs?
3x=y'=3^x(ln3)<<< what is this - 2 "=" signs?

=3x^2/3^x(ln3)

You need to apply:

\(\displaystyle f'(\frac{u}{v})\, = \, \frac{u'\cdot v \, - \, v'\cdot u}{v^2}\)
 
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