(a) Using angle sum property of a quadrilateral,
50°+130°+120°+x=360°
⇒ 300°+x=360°
⇒ x=360°-300° ⇒x=360°
(b) Using angle sum property of a quadrilateral,
90°+60°+70°+x=360°
⇒ 220°+x=360°
⇒x=360°-220° ⇒x=140°
(c) First base interior angle = 180°-70°=110°
Second base interior angle = 180°-60°=120°
There are 5 sides, = 5 n
∴ Angle sum of a polygon = (n-2)x180°
= (5-2)x180°=3×180 =540°
∴ 30°+x+110°+120°+x=540°
⇒ 260°+2x+540° ⇒2x=540°-260°
⇒ 2x=280° ⇒x=140°

(d) Angle sum of a polygon = (n-2)x180°
= (5-2)x180°= 3×180° = 540°
∴ x+x+x+x+x =540°
⇒ 5x=540° ⇒ x=108°
Hence each interior angle is 108°

Class 8 Maths Chapter 3 Exercise 3.1 Solution in Video