Reference Angles and Triangles

                    Lesson 1


                                                            Problem:    The value of Sin 390 is equal to?



                                                            Solution     The value of Sin 390 is equal to

                                                            Step 1:        


                                                            Solution     The angle is one complete revolution plus 30.

                                                            Step 2:           


                                                            Solution     Look at the triangle, it can be seen that Sin 390 = and that Cos 60

Step 3: (in the same triangle) is that same result.                                                             


                                                            Solution     Answer: Sin 390 = Cos 60

                                                            Step 4: 



                                                            Try two practice problems:  



The value of sin 420 is equal to ?


Write sec -250 as a positive acute angle.










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