From the graph of the sin(x) function between 0 and PI/2 if we take 3 points
A(x, sin(x)), origin and (PI/2,1) there will take shape 1 triangle and otherwise 1 triangle and 1 trapezium. If we consider that the area of the first triangle is smaller then the sum of the second triangle and the trapezium we will find the relation (well know!!!)
sin(x)>=2*x/PI. After we replace in this relation the angle A,B, and C and sum this 3 relation we will find sin(A) + sin(B) + sin(C) > 2

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