The diameter of a circle whose area is equal to the sum of the areas of the two circles of radii 40 cm and 9 cm is:
82 cm
Radius (r1) of 1st circle = 40 cm
Radius (r2) or 2nd circle = 9 cm
Let radius of 3rd circle be r
Area of 1st circle
Area of 2nd circle
Given that
Area of 3rd circle = area of 1st circle + area of 2nd circle
But radius cannot be negative, so radius of the third circle is 41 cm. Hence, its diameter is 82 cm.