How do you evaluate #arcsin(sin((5pi)/3)) #?
The arcsin function is the inverse function of sin. You can think of it in the same way that taking away a number is the opposite of adding it.
Your question is like asking "What's 5 + 2 - 2?". It's just the same as what you started with - we don't need to figure out what 5 + 2 is because we know that we're just going to take away 2 again, so we know it's 5.
In the same way, we don't need to work out what
Hope this helps :-)