HomeLearn Fast select Course
Show Unit/ChapterChange UnitChange SubjectLast Menu
ICSE-VIII-Mathematics

16: Understanding Shapes (Including Polygons) Class 8 Maths

with Solutions - page 3
Qstn# B-3 Prvs-QstnNext-Qstn
  • #3
    Find the number of sides in a regular polygon, if its each exterior angle is : (i) 1/3 of a right angle (ii) two-fifth of a right-angle. (i) 1/3 of a right angle (ii) two-fifth of a right-angle.
    Ans : (i) Each exterior angle = 1/3 of a right angle
    = 1/3 ×90
    = 30°
    Let number of sides = n
    ∴ 360˚/n = 30˚
    ∴ n = 360˚/30˚
    ⇒ n = 12 (ii) Each exterior angle = 2/5 of a right-angle
    = 2/5 × 90˚= 36˚
    Let number of sides = n
    ∴ 360˚/n = 36˚
    ⇒ n = 360˚/36˚
    ⇒ n = 10 (i) Each exterior angle = 1/3 of a right angle
    = 1/3 ×90
    = 30°
    Let number of sides = n
    ∴ 360˚/n = 30˚
    ∴ n = 360˚/30˚
    ⇒ n = 12 (ii) Each exterior angle = 2/5 of a right-angle
    = 2/5 × 90˚= 36˚
    Let number of sides = n
    ∴ 360˚/n = 36˚
    ⇒ n = 360˚/36˚
    ⇒ n = 10
  • #3-i
    1/3 of a right angle
    Ans : Each exterior angle = 1/3 of a right angle
    = 1/3 ×90
    = 30°
    Let number of sides = n
    ∴ 360˚/n = 30˚
    ∴ n = 360˚/30˚
    ⇒ n = 12
  • #3-ii
    two-fifth of a right-angle.
    Ans : Each exterior angle = 2/5 of a right-angle
    = 2/5 × 90˚= 36˚
    Let number of sides = n
    ∴ 360˚/n = 36˚
    ⇒ n = 360˚/36˚
    ⇒ n = 10