Decimal representations of some basic angles: As a last quick topic let's note that it will, on occasion, be useful to remember the decimal representations of some basic angles. So following they are,

π/2= 1.5708                        π= 3.1416              3π/2 =4.7124 2π = 6.2832

By using these we can rapidly see that cos^-1(  3/4)have to be in the first quadrant since 0.7227 is among 0 and 1.5708. It will be of great help while we go to find out the remaining angles

Hence, once again, we can't stress sufficient that calculators are significant tools which can be of tremendous help to us, however it you don't understand how they work you will frequently get the answers to problems wrong.