I really dont know how to start this questions, please help me. Thank you in advance for all your help & support.
Determine if each of the following CT signals is periodic. If periodic find it period.
a) x(t)=2sin(10 t-30degrees)
b) x(t) = 2 cos ( 2 t)
c)x(t) = 2 sin ( t)
d) x(t) = 2 cos (t+ 60degrees)
If true, I suggest that you review some websites found by Google: Google
For example, About trigonometric functions
Getting a hold of a textbook that covers basic trigonometric functions would also be prudent.
Do you know the difference between degrees and radians? If not, I suggest you review that material as well.
I think it's perfectly reasonable to direct you to resources and request that you review them so that you might be in a better position to make inroads into the questions you posted. After doing so, you can still ask for help, but you'll be able to be more specific on exactly where you're stuck.
Having reviewed your post history, I can surmise from the questions you've posted that you have studied complex numbers, differential equations, calculus of one and several variables, analysis etc.
But you're claiming to have no knowledge of trigonometric functions ....