Students can go through AP Board 8th Class Maths Notes Chapter 9 Area of Plane Figures to understand and remember the concepts easily.

## AP State Board Syllabus 8th Class Maths Notes Chapter 9 Area of Plane Figures

→ Area of a triangle = \(\frac{1}{2}\) × base × height = \(\frac{1}{2}\) bh

→ Area of a quadrilateral = \(\frac{1}{2}\) × length of a diagonal × Sum of the lengths of the perpendiculars drawn from the remaining two vertices on the diagonal

= \(\frac{1}{2}\) d(h_{1} + h_{2})

→ Area of a trapezium = \(\frac{1}{2}\) × sum of the lengths of parallel sides × distance between them

= \(\frac{1}{2}\) h(a + b)

→ Area of a rhombus = Half of the product of diagonals = \(\frac{1}{2}\) d_{1}d_{2}

→ Angle at the centre of a circle = 360°

→ Area of a circle = πr^{2}

Where ‘r’ is the radius of the circle, π = \(\frac{22}{7}\) or 3.14 nearly

→ Circumference of a circle = 2πr

→ Area of a circular path (or) Area of a Ring = π(R^{2} – r^{2}) or π(R + r) (R- r)

When R, r are radii of outer circle and inner circle respectively.

→ Width of the path w = R – r

→ Area of a sector A = \(\frac{x^{\circ}}{360^{\circ}}\) × πr^{2} where x° is the angle subtended by the arc of the sector at the center of the circle and r is radius of the circle. (OR) A = \(\frac{lr}{2}\) where Tis thdength of the arc.

Length of the arc of a sector = \(\frac{x^{\circ}}{360^{\circ}}\) × 2πr