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 \[\boxed{\tan \left(42^\circ\right)=\frac{b}{a}}\].