How to add or subtract radians? for example: pi/3 - pi/6 ?

Pi/3 - pi/6

Adding or subtracting radians is solve the same way we add and subtract fractions.

1st step, find the least common denominator of the fractions.
3: 3, 6
6: 6  LCD is 6.

Multiply each fraction by a fraction that will result of a denominator of 6.

pi/3 * 2/2 = 2pi/6
pi/6 * 1/1 = pi/6

2pi/6 - pi/6 = (2pi - pi) / 6 = pi/6

So, pi/3 - pi/6 = pi/6.

The correct answer is -20y