Calculation: uXmYYS - 1

 
 a
/ sin(A)
  = 
 2* R
 
 a
/ sin(A)
 =  2* R$$\frac{a}{sin(A)}$$ = $$2\cdot R$$
a =  2* R* sin(A)$$a$$ = $$2\cdot R\cdot sin(A)$$