Problem
Based on the figure, select all true equations. \[ \begin{array}{l} \cos \left(42^{\circ}\right)=\frac{b}{c} \\ \cos \left(48^{\circ}\right)=\frac{b}{c} \\ \sin \left(42^{\circ}\right)=\frac{b}{c} \\ \sin \left(48^{\circ}\right)=\frac{b}{c} \\ \tan \left(42^{\circ}\right)=\frac{b}{a} \\ \tan \left(48^{\circ}\right)=\frac{b}{b} \end{array} \]
Solution
Step 1 ：Given a right triangle with angle measures 42°, 48°, and 90°, we can use trigonometric functions to find the true equations.
Step 2 ：Using the trigonometric functions, we find the true equations to be: \[\boxed{\cos \left(42^\circ\right)=\frac{b}{c}}\], \[\boxed{\sin \left(48^\circ\right)=\frac{b}{c}}\], and \[\boxed{\tan \left(42^\circ\right)=\frac{b}{a}}\].
