Use an addition or subtraction formula to find the exact value of $\displaystyle {\cos{{\left(-{\frac{{\pi}}{{{12}}}}\right)}}}={\frac{{\sqrt{{{A}}}{\left(\sqrt{{{B}}}+{1}\right)}}}{{{4}}}}$.
$\displaystyle {A}=$ Preview Question 6 Part 1 of 2   ;
$\displaystyle {B}=$ Preview Question 6 Part 2 of 2   .