(A) If a is one side of a square, then the area of the square is a
2. If D and r are the diameter and the radius of a semicircle, respectively, then the area of the semicircle is


r
2, where r =

.
Thus, the diameter of the semicircle = NO = 7 cm
Radius of the semicircle =

cm
Area of the semicircle =

cm
2 =

cm
2 =

cm
2Now, the area of the square = 7
2 cm
2 = 7

7 = 49 cm
2
Area of the shaded portion = (49 –

) cm
2 = 49

cm
2= 49

cm
2 (B) If 'a' is the side of the square, then area of the square = a
2If 'r' is the radius of the circle, then area of a quadrant of the circle =
Thus, the area of the square OABC = (5 cm)
2 = 5 cm

5 cm = 25 cm
2And the radius of the circle = OA = 5 cm
Thus, the area of the quadrant of the circle =

cm
2=

×

× 5 × 5
=

×

× 25 cm
2=

cm
2 Hence, the area of the shaded region = area of square OABC -

x area of circle =

(C) In an equilateral triangle, all the sides are equal. If D and r are the diameter and the radius of the semicircle, respectively, then r =

and the area of the semicircle is

.
So, in the given figure, AB = BC = CA = 6 cm
Thus, the diameter of the semicircle = BC = 6 cm
Radius of the semicircle = 6 ÷ 2 cm = 3 cm
Therefore, the area of the shaded portion = Area of the semicircle
=

cm
2