Find sin ?/2 and tan ?/2

Question

If cos θ= -1/5 and 90°< θ< 180°

Answer 1

If cos θ= -1/5 and 90°< θ< 180° is given, so all you have to do is

1) realize that the half angle is in Quadrant I

2) use formulas for half angles, e.g. cos(½θ) = √(½(1+cos θ)) & sin(½θ) = √(½(1-cos θ))

 

Have fun simplifying!  Note: you can always check, using the calculator (in decimal).