Heloo, Keith!

The formulas are:

. .

. .

and we must choose the sign carefully.

Use the half angle formulas:

is in Quadrant 3, where sine isnegative.

is in Quadrant 2, where sine ispositive.

is in Quadrant 3, where cosine isnegative.

is in Quadrant 1, where cosine ispositive.