Hello, I just started this topic and is already struggling with a few questions, that I need help kindly need help with, as I am unable to get the correct answer.

Question 1) Find the exact value of the following:

a. Cos315

I thought the method to this was to subtract it with the nearest degree.

Therefore being 270=315-270

=cos45.

And according to the table I was given cos 45 is √2/2.

http://moodle.tbaisd.org/file.php/87...atio_table.gif

However the answer is 1/√2

Similarly

b. Sin240

I thought the answer would be 270(nearest)-240=30

Thus Sin30

=-√1/2

However the answer is -√3/2

Can you please explain how they get this answer. Thanks