Here's the question you clicked on:
sara1234
Help please ?
you are looking for the number between 0 and \(\pi\) whose cosine is \(\frac{1}{2}\)
if you still have that cheat sheet, look at the place on the upper half of the unit circle where the second coordinate is \(\frac{1}{2}\)
ok here is the picture |dw:1351127015253:dw|
in this picture, \(\theta=\arctan(2)\) an angle whose tangent is 2 since tangent is "opposite over adjacent" i labelled the opposite side 2 and the adjacent side 1
the hypotenuse we find by pythagoras, it is \(\sqrt{1^2+2^2}=\sqrt{1+4}=\sqrt{5}\)
and using sine as "opposite over hypotenuse" we see that the sine of the angle is \[\frac{2}{\sqrt{5}}\]