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(h1 + h2)

→ 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 = $$\frac{1}{2}$$ d1d2

→ Angle at the centre of a circle = 360°

→ Area of a circle = πr2
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(R2 – r2) 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 = $$\frac{x^{\circ}}{360^{\circ}}$$ × πr2 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