3. Find the greatest and least values of the function $y=3 x^{4}-6 x^{2}+4$ on the interval $[-1 ; 3]$.
Solution: $\quad y=3 x^{4}-6 x^{2}+4 \quad$ on $\quad[-1 ; 3], \quad y^{\prime}=12 x^{3}-12 x=12 x\left(x^{2}-1\right), \quad x=0, \pm 1$, $y(-1)=1, y(3)=193, y(0)=4, y(1)=1$. Answer: $y(-1)=y(1)=1, y(3)=193$.