Hi, I am a very elderly person, I have long forgotten my mathematics but i now find the need to solve a simple equation:

In any right angle triangle having sides a,b,c and angles A,B,C, I want to solve for "c".

in my example, a=3. I think c = a cos A but no matter how many times I enter this data , I can not get the answer which is c = 5.

Please lead me through the actual steps to solve this using an engineering calculator.