Let x cm be one of the equal sides of an isosceles triangle.
Given that the perimeter of the isosceles triangle = 18 cm
Then, x + x + 8 =18
2x = (18 – 8) = 10 cm
2x = 10
x = 5 cm
Area of the figure formed = Area of the square + Area of the isosceles triangle
= (side of square)2 + (base x √[(equal side)2 – x (base)2]
= 82 + (8) x √ [52 – x 82]
= 64 + 4 x √ [25 – x 64]
= 64 + 4 x √ (25 – 16)
= 64 + 4 x √9
= 64 + 4 x 3
= 64 + 12
= 76 cm2
