Expand the following: \begin{align} F_b &= \cssId{Step1}{\frac{v^2_0 }{2gS_s}mg·cos α} \\[3px] &\cssId{Step2}{{} = \frac{v^2_0 m·cos α }{2S_s}} \\[3px] &\cssId{Step3}{{} = Equiation..15..} \\[3px] \end{align}