find the exact value of the remaining trigonometric functions of θ. cosθ=(4)/(5) , 270°

Question

find the exact value of the remaining trigonometric functions of θ.                                                                cosθ=(4)/(5) , 270° < θ < 360°

rulnick · Answer

theta = acos(4/5) = 36.9 degrees (rounded)
so the theta you want is 360-36.9 = 323.1 degrees (rounded)

hero · Answer

not exactly an exact value, but okay

rulnick · Answer

oh, my mistake. thanks, Hero.  I'll get the exact value.

hero · Answer

Yeah, if it hadn't said "find exact value", I would have already posted the solution

rulnick · Answer

Well, the best we can do is 360 - acos(4/5), or am I missing an obvious closed form for acos(4/5) ... ?