Trigonometric functions of the acute angle Find the other five trigonometric functions of the acute angle A, given that:
\begin{align}
&\text{a)}\ \ \sec A = 2  \\[15pt]
&\text{b)}\ \ \cos A = \frac{m^2 - n^2}{m^2 + n^2}
\end{align}
Help me. I don't know how to solve this one. Thanks.

Honestly, I suspect that equation b is a red herring.
\begin{align}
\cos{A}
&=\frac{1}{\sec{A}}\\
&=\frac{1}{2}
\end{align}
\begin{align}
\sin{A}
&=\sqrt{1-\cos^2{A}}\\
&=\frac{\sqrt{3}}{2}
\end{align}
\begin{align}
\tan{A}
&=\frac{\sin{A}}{\cos{A}}\\
&=\sqrt{3}
\end{align}
\begin{align}
\csc{A}
&=\frac{1}{\sin{A}}\\
&=\frac{2}{\sqrt{3}}\\
\end{align}
\begin{align}
\cot{A}
&=\frac{1}{\tan{A}}\\
&=\frac{1}{\sqrt{3}}\\
\end{align}
