How do you find the exact value of #arccos (-sqrt3/2)#?
The angle whose cosine is
Draw an equilateral triangle.
Cut it in half .
The angles in this right angle triangle are 30 ,60, 90
If the hypotenuse is length 2 then the shortest side is 1 and from Pythagoras the other side is
So the angle whose cosine is
Now sketch the cosine graph.
From this you can find the angle whose cosine is
Is 150 degrees or