Class Notes NCERT Solutions for CBSE Students
QUADRILATERALS
Quadrilaterals are four sided polygons. Here are some special quadrilaterals.
Angles of Quadrilaterals
Look at these quadrilaterals.
Each has a diagonal that divides the quadrilateral into two triangles.
We know that the sum of angles in a triangles is 180°.
Since each quadrilateral has two triangles, the sum of angles in the quadrilateral = 180° × 2 = 30°.
Square ABCD has ∠A = ∠B = ∠C = ∠D = 90°
Sum of the angles in Δ ABD = 180° (90° + 45° + 45°)
Sum of the angles in ΔBCD = 180° (90° + 45° + 45°)
Sum of the angles in ΔABD + Sum of the angles ΔBCD = 360°
Sum of the angles in square ABCD =360°
You can check this out for yourself.
1. Draw and cut out a quadrilateral.
If you know the measure of three angles of a quadrilateral, you can find the fourth angle.
∠a + ∠b + ∠c = 50 + 80 + 120 = 250°
∠d = 360 – 250 = 110°
