$2\mathrm{.}6[21]$ Derive equation $(2\mathrm{.}80).$

$2\mathrm{.}7[24]$ Describe $($or program$)$ an algorithm that extracts the equivalent angle andaxis of a rotation matrix. Equation $(2\mathrm{.}82)$ is a good start, but make sure that your

algorithm handles the special cases $8=0\backslash$deg and $9=180\backslash$deg $.$