Krishna
0

Step 1: Note down the given equation and known about the complimentary angles

             GIVEN:   \cos 12\degree - \sin 78\degree


Step 2:  Using the trigonometric ratio for complementary angles,

              NOTE: we know that, \cos A = \sin (90\degree - A)


               EXAMPLE: = \cos 12\degree = \sin (90\degree - 12\degree)


                                  = \cos 12\degree = \sin 78 \degree.............(1)


Step 3: Insert the known values and solve for the unknown value.

             EXAMPLE: =   \cos 12\degree - \sin 78\degree


                                =   \sin 78\degree - \sin 78\degree    [since equation (1)]

                                

                                 =  0