Page 232 - Start Up Mathematics_8 (Non CCE)

AT a Glance

1. A plane surface is an unobstructed shape like a sheet of paper. A plane has no thickness and it extends
indefinitely. If a number of points on a plane surface are joined without breaking (i.e., without lifting the
pencil) and without retracing any part of the path except single points, the curve so formed is called a
plane curve.
2. A convex polygon is a simple polygon where each interior angle is less than 180° and the segment
connecting any two points in the interior of the polygon is wholly contained in the interior of the polygon.
3. A concave polygon is a polygon which has at least one interior angle greater than 180° and it is always
possible to locate two points in the interior of a concave polygon so that the segment connecting them is
not wholly contained in its interior.
4. In a regular polygon, all sides are of the same length and all angles are of the same measure. A polygon
which is not regular is an irregular polygon.

Types of quadrilaterals

All angles equal Two pairs of angles equal One pair of angles equal
• All sides equal • All sides equal • Adjacent sides equal
• Both pairs of opposite • Both pairs of opposite • No parallel sides
sides parallel sides parallel
• Each angle = 90°

Square Rhombus Kite

• Opposite sides equal • Opposite sides equal • May have equal sides
and parallel and parallel • Equal angles = 90°
• Each angle = 90°

Rectangle Parallelogram Right trapezium
No angles equal
• One pair of opposite • No sides or angles equal
sides equal • One pair of opposite sides is parallel

Isosceles trapezium Trapezium

Review Exercises

Multiple ChoiCe Questions

1. In quadrilateral FISH, –FIS = –ISH = –SHF and –HFI = 150º, then –FIS = ?
(a) 80º (b) 70º (c) 75º (d) 85º

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