Factorize each of the following algebraic expression:

$49-a^{2}+8 a b-16 b^{2}$

$=49-\left(\mathrm{a}^{2}-8 \mathrm{ab}+16 \mathrm{~b}^{2}\right)$

$=49-\left[\mathrm{a}^{2}-2 \times \mathrm{a} \times 4 \mathrm{~b}+(4 \mathrm{~b})^{2}\right]$

$=7^{2}-(\mathrm{a}-4 \mathrm{~b})^{2}$

$=[7-(\mathrm{a}-4 \mathrm{~b})][7+(\mathrm{a}-4 \mathrm{~b})]$

$=(7-\mathrm{a}+4 \mathrm{~b})(7+\mathrm{a}-4 \mathrm{~b})$

$=-(\mathrm{a}-4 \mathrm{~b}-7)(\mathrm{a}-4 \mathrm{~b}+7)$

$=-(\mathrm{a}-4 \mathrm{~b}+7)(\mathrm{a}-4 \mathrm{~b}-7)$