Algebraic Expressions & Formulae

Names of angles

acute angle $(<90^\circ)$
right angle $(90^\circ)$
obtuse angle $(90^\circ<\theta<180^\circ)$
reflex angle $(>180^\circ)$

Types of angles

1. $\angle$ on a st. line
2. $\angle$ at a pt.
3. vert. opp. $\angle$
4. alt. $\angle$
5. corr. $\angle$
6. int. $\angle$

Types of polygons

$\begin{array}{|c|c|} \hline \textbf{No. of sides}& \textbf{Polygons} \\\hline \text{3} & \text{triangle} \\\hline \text{4} & \text{quadrilateral} \\\hline \text{5} & \textbf{pent}\text{agon} \\\hline \text{6} & \textbf{hex}\text{agon} \\\hline \text{7} & \textbf{hept}\text{agon} \\\hline \text{8} & \textbf{oct}\text{agon} \\\hline \text{9} & \textbf{non}\text{agon} \\\hline \text{10} & \textbf{dec}\text{agon} \\\hline \end{array}$

Sum of interior & exterior angles

Sum of interior angles $=(n-2)\times180^\circ$
Sum of exterior angles $=360^\circ$