Find (tan20°+tan10°)/(1-tan20°tan10°)=?
There is a trig identity tan (a+b) = (tan a + tanb )/(1- tan a tan b)
so this equals tan (20 + 10) = tan30 = sin 30 / cos 30 = 1/2 / sqrt3/2 = 1/sqrt3 = sqrt3/3
+37170 
