Perimeter and Area

Area = ½ × base × height. Height must be perpendicular to the base. Any side can be taken as base. The triangle can be right-angled, acute or obtuse — formula remains same. For right triangle: area = ½ × leg1 × leg2.

Area = base × height. Height is perpendicular distance between parallel sides (NOT the slant side). A rectangle is a special parallelogram with height = breadth. Important: diagonal of parallelogram divides it into 2 equal triangles.

Circle: all points at equal distance (radius r) from center. Circumference (perimeter) = 2πr. Area = πr². π ≈ 22/7 ≈ 3.14159. Diameter d = 2r. Semi-circle: perimeter = πr + 2r, area = πr²/2.