\(A=cosy+siny.\dfrac{siny}{cosy}=\dfrac{cos^2y+sin^2y}{cosy}=\dfrac{1}{cosy}\)
\(B=\sqrt{1-cos^2b}=\sqrt{sin^2b}=\left|sinb\right|\)
\(C=sina.\sqrt{1+\dfrac{sin^2a}{cos^2a}}=sina\sqrt{\dfrac{cos^2a+sin^2a}{cos^2a}}=sina\sqrt{\dfrac{1}{cos^2a}}=\dfrac{sina}{\left|cosa\right|}=\pm tana\)