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Angles in Shapes

Angles in a Triangle | Angles in a Quadrilateral

Angles in a Triangle

The sum of the angles in a triangle is 180^o.

This property can be used to solve problems on angles.

Example 1: Given triangle ABC with angle BÂC=100^o and angle BĈA=20^o, Calculate angle

The method is to add the two angles given and subtract this total from 180° .

Note: Reasons are often asked for and should be given briefly, in brackets.

Example 2: Given triangle LMN with angle

=50° and LM= LN, calculate angle

, angle

and angle

angles in shapes3

Example 3: Given triangle PQR with

=30°, the line RS is parallel to PQ and

=90°. Calculate angles

and

Angles in a Quadrilateral

The sum of the angles in a quadrilateral is 360°.


Again this property can be used to calculate missing angles.
Example 1: Given the quadrilateral PQRS, calculate angle .


Example 2: Given the parallelogram LMNO, with angle LÔN = 70°. Calculate angles , and .