You should know the sines, cosines and tangents that come from
30-60-90 right triangles and isosceles right triangles. Remember that
π/6 radians is 30 degrees, π/4 radians is 45 degrees, and
π/3 radians is 60 degrees:
sin(π/6)=1/2;
cos(π/6)=√3/2;
tan(π/6)=√3/3
sin(π/4)=√2/2;
cos(π/4)=√2/2;
tan(π/4)=1
sin(π/3)=√3/2,
cos(π/3)=1/2;
tan(π/3)=√3
From these values, we can figure out the trig functions of common angles
in the second, third and fourth quadrant. These are developed in the
following two videos: