1. Problem statement:
Find the stationary point(s) of the curve $y=(3x^2+8)^{5/3}$ and determine their nature.
2. Formula and rules used:
We use the chain rule: if $y=u^n$ then $y'=n u^{n-1}u'$.
Important rule: $3x^2+8>0$ for all real $x$, so $(3x^2+8)^{2/3}>0$ for all real $x$ and fractional powers are real here.
3. Compute the derivative (showing intermediate algebra):
Start with $y=(3x^2+8)^{5/3}$.
Differentiate using the chain rule: $y'=\frac{5}{3}(3x^2+8)^{2/3}\cdot(6x)$.
Simplify the numeric factor with cancellation: $\frac{5}{3}\cdot 6 = 5\cdot\frac{\cancel{6}}{\cancel{3}} = 5\cdot 2 = 10$.
Therefore $y'=10x(3x^2+8)^{2/3}$.
4. Solve $y'=0$ to find stationary points:
Set $10x(3x^2+8)^{2/3}=0$.
Divide both sides by 10 showing cancellation: $\frac{\cancel{10}x(3x^2+8)^{2/3}}{\cancel{10}}=0$.
So $x(3x^2+8)^{2/3}=0$.
Because $(3x^2+8)^{2/3}>0$ for every real $x$, the only solution is $x=0$.
Thus the stationary point abscissa is $x=0$.
5. Find the corresponding $y$ value:
Evaluate $y(0)=(3\cdot 0^2+8)^{5/3}=8^{5/3}$.
Write $8=2^3$ and simplify: $8^{5/3}=(2^3)^{5/3}=2^5=32$.
Therefore the stationary point is $(0,32)$.
6. Determine the nature via the second derivative test:
Start from $y'=10x(3x^2+8)^{2/3}$ and apply the product rule.
Compute $y''=10(3x^2+8)^{2/3}+10x\cdot\frac{2}{3}(3x^2+8)^{-1/3}\cdot(6x)$.
Simplify the factor $\frac{2}{3}\cdot 6x$ with cancellation: $\frac{2}{3}\cdot 6x = 2\cdot\frac{\cancel{6}x}{\cancel{3}} = 4x$.
So $y''=10(3x^2+8)^{2/3}+10x\cdot 4x(3x^2+8)^{-1/3} = 10(3x^2+8)^{2/3}+40x^2(3x^2+8)^{-1/3}$.
Factor out $(3x^2+8)^{-1/3}$: $y''=(3x^2+8)^{-1/3}\bigl(10(3x^2+8)+40x^2\bigr)$.
Simplify inside: $10(3x^2+8)+40x^2=30x^2+80+40x^2=70x^2+80$.
Thus $y''=(3x^2+8)^{-1/3}(70x^2+80)$.
Evaluate at $x=0$: $y''(0)=8^{-1/3}\cdot 80$.
Since $8^{1/3}=2$, $y''(0)=80/2=40>0$.
A positive second derivative means the stationary point is a local minimum.
7. Final answer (concise):
The curve has a single stationary point at $(0,32)$, and it is a local minimum.
Stationary Point 522771
Step-by-step solutions with LaTeX - clean, fast, and student-friendly.