45 45 90 triangle find values of sine cosine and tangeant of 45

In this case you could obtain the values of the trig functions in many ways, including using a calculator, using a table of trig functions (old fashioned!), using an illustration which shows various common angles (including 45 and 90 degrees) and their related trig functions.  Or you could memorize the values of the sine, cosine and tangent functions, which I highly recommend.

                         1
sin 45 deg = -----------  
                      sqrt(2)
              
                          1
cos 45 deg = ----------
                      sqrt(2)

tan 45 deg = 1/1 = 1

cos 90 deg = 0
sin 90 deg = 1
tan 90 deg:  undefined