The value of (tan50° + tan10°)/(1 − tan50°·tan10°) is:

The expression is exactly tan(A + B) with A = 50° and B = 10°, so it equals tan60° = √3 ≈ 1.732. Arithmetic check: (1.1918 + 0.1763)/(1 − 0.2101) = 1.3681/0.7899 = 1.732. Reading the signs as the subtraction formula would answer tan40° ≈ 0.839; 1/√3 = tan30° would need the two angles to add to 30°; and 3 squares the answer.