Consider the polar graph $r={?}^{t}7+cos(7).$

$($a$)$ Find the slope of the tangent line when $=\frac{}{2}.$

$($b$)$ The equation of the tangent line when $=\frac{}{2}$ is of the form $y=mx+b.$ What is the value of $b?$

Enter your answer symbolically, as in these examples

Enter your answer symbolically, as in these examples