Two trigonometric help

Question

Answer 1

(4)

The trigonometric function value of that means angle A lies in IV quadrant.

 Using the Pythagorean identity , obtain

Because cos A > 0 in Quadrant IV, you can use the positive root to obtain .

.

The trigonometric function value of that means angle B lies in II quadrant.

Using the Pythagorean identity , obtain

Because sin B > 0 in Quadrant II, you can use the positive root to obtain .

.

                                                                  

                                                                  

                                                                   .

Option H is correct answer.

Answer 2

(5) The double angle formula for cosine function : .

The trigonometric function value of that means angle lies in III quadrant.

Substitute the value of in .

                 

                 

                 

                  .

Option C is correct answer.