Question

Determine two angles between 0° and 360° that have a cosine of negative root3/2 without using a calculator

Answer 1

Answer:

150° and 210°

Step-by-step explanation:

1) to drow a circle with radius=1 in the system of coordinates like in the attached picture;

2) to mark point (-√3/2)≈-0.866 on X-axis (in the picture it is the point M);

3) to graph line AB through point M, the line AB || Y-axis and the points A and B are on the circle with radius=1;

4) to measure the angles ∠ROA and ∠ROB (the points are marked with red colour);

5) finally, m(∠ROA)=150°; m(∠ROB)=210°.