Lets consider these three shapes.
1. The large triangle QBA.
Its base QA is 1 unit.
The line AB can be found knowing that Tan(x) = AB/QA, but AQ is 1. Therefore AB = Tan(x)
This means Area = half x base x height = 1/2 x 1 x tan(x) = 1/2 tan(x)
2. The area of the small triangle QPA can be found using the formula
Area = 1/2 ab sinC. in this case both a and b are 1 since we are in the unit circle.
this means Area = 1/2 sin(x)
3. The sector has area (in radians) of x/2π×πr^2
