Find the two possible values for theta between 0 and 2 pi or

Find the two possible values for theta between 0 and 2 pi (or 360 degree): cos theta = 0.309 tan theta = -1.732

Here are the answers:.

I have deliberately retained the answers in degrees

a) arccos .309 = cos¹ .309 = 72° 0\' 3.686\"
= 72° + k×360° (k=..-1,0,1,..)
= -288°, 72°

b) arctan -1.732 = tan¹ -1.732
= -60°+k×180° (k=..-1,0,1,..)
= 120°,300°