Question

tan(3arc cos3/4)?

=3cos3/4
=cos=4

sqrt17/4 = tan

Answer 1

arccos3/4, the angle whose cosine is 3/4 is 41.4 degrees. Three times that angle is 124.2 degrees.
The tangent of that angle is -1.467

I don't know what your last three equations are about. They don't make mathematical sense.