Step 1: Draw a special right triangle with a 60° angle.

            NOTE: A special right triangle 30\degree-60\degree-90\degree.                                    

                  It's sides are 1, 2 and \sqrt{3}


Step 2: Recall the definition of cosine and calculate \cos\ 60\degree

             DEFINITION: The cosine (cos) of an angle in a right triangle is a ratio.

                            It is the length of the adjacentleg (adj) divided by the length of

                            the hypotenuse (hyp).

             NOTE:  The length of the adjacent  side is  1

                                length of the hypotenuse is 2




Step 3: Calculate \cos\ 30\degree

                 The length of the adjacent side is   \sqrt{3}

                   length of the hypotenuse is 2

                    \cos30\degree=\ \frac{adj}{hyp}