Let us calculate the area of a circular region circumscribe a triangle of which sides are 3 cm, 4 cm and 5 cm.
By the pythagoras theorem,
32 + 42 = 9+16 = 25
And 52 = 25
⇒ The given triangle forms a right angled triangle
∴ BC will act as the diameter of the circumcircle centered at O.
Diameter = 5 cm
⇒ Radius = 2.5 cm
∵ Area of a circle = πr2
⇒ Area of the circumcircle 
⇒ Area of circumcircle = 19.64 cm2
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