Chapter 4, Problem 57RE

In each part, use a graphing utility to estimate the absolute maximum and minimum values of $f,$ if any, on the stated interval, and then use calculus methods to find the exact values.

(a) $f\left(x\right)={\left(x^2-1\right)}^2;\left(-\infty ,+\infty \right)$

(b) $f\left(x\right)=x/\left(x^2+1\right);\left[0,+\infty \right)$

(c) $f\left(x\right)=2\sec x-\tan x;\left[0,\pi /4\right]$

(d) $f\left(x\right)=x/2+\ln \left(x^2+1\right);\left[-4,0\right]$