Edexcel C3 - Inverse Trigonometric Functions Questions Ex 6E

I don't understand how to even do question 1 of this exercise, or how the examples work. For example 1, the question (a) is work out the value, in radians of arcsin(-root2/2). The example seems to just state without explanation that this is equal to pi/4. I don't really see how it helps to understand how to do the questions in 6E.

Without using a calculator, work out the values ,in terms of pi, of:

Arccos0
Arcsin1
Arctan-1
Arcsin-1/2

And so on... Can anybody explain how to work these out?

You'll need to memorise the values of trigonometric functions with argument 0, 30, 45, 60, and 90 degrees.

Once you know those, the questions are asking you:

arccos 0 - what number do you need to take the cos of to give you 0? Hmm, well I know that cos 90 = 0 so arccos 0 = 90.