Question:
The maximum value of $[x(x-1)+1]^{\frac{1}{3}}, 0 \leq x \leq 1$ is
(A) $\left(\frac{1}{3}\right)^{\frac{1}{3}}$
(B) $\frac{1}{2}$
(C) 1
(D) 0
Solution:
Let $f(x)=[x(x-1)+1]^{\frac{1}{3}}$.
$\therefore f^{\prime}(x)=\frac{2 x-1}{3[x(x-1)+1]^{\frac{2}{3}}}$
Now, $f^{\prime}(x)=0 \Rightarrow x=\frac{1}{2}$
Then, we evaluate the value of $f$ at critical point $x=\frac{1}{2}$ and at the end points of the interval $[0,1]\{$ i.e., at $x=0$ and $x=1\}$.
$f(0)=[0(0-1)+1]^{\frac{1}{3}}=1$
$f(1)=[1(1-1)+1]^{\frac{1}{3}}=1$
$f\left(\frac{1}{2}\right)=\left[\frac{1}{2}\left(\frac{-1}{2}\right)+1\right]^{\frac{1}{3}}=\left(\frac{3}{4}\right)^{\frac{1}{3}}$
Hence, we can conclude that the maximum value of f in the interval [0, 1] is 1.
The correct answer is C.