1.

prove that cosAcos(30-A)cos(30+A)= 1/4 cos3A

Hence, evaluate cosAcos(30-A)cos(30+A) when A= 170 degree;

give your answer in exact value.

2.

Assuming r is positive, find r and the value of θ between -180degree and 180 degree which satisfy the questions:

r cos θ= -6 and r sin θ= 1.5

Give your answer to the nearest minute.