trigonometry homework for ROEL_MATHPHYSICSCHEM

1) verify the identity:

sinx tanx + cos x = sec x

2) verify the identity

cos x divided by 1+ sin x  +  1 + sin x divided by cos x = 2 sec x

3) find the exact value by using a sum or difference identity 

sin (60 degrees - 45 degrees)

4) find the exact value of the expression

cos (155 degrees) cos (35 degrees) + sin (155 degrees) sin (35 degrees)

5) use a half-angle formula to find the exact value of the expression

cos  3pi divided by 8