Cambridge International Mathematics

100 Lines, angles and polygons (Chapter 4)

3 State whether the following statements aretrueorfalse:

a The sum of the angles of a triangle is equal to two right angles.

b A right angled triangle can contain an obtuse angle.

c The sum of two angles of a triangle is always greater than the third angle.

d The two smaller angles of a right angled triangle are supplementary.

e A concave triangle is impossible.

4 Find the values of the unknowns in each triangle, giving a brief reason for each answer:

abc

de f

5 The three angles of a scalene triangle are xo,(x¡12)o and(2x+6)o. What are the sizes of these

angles?

Anisosceles triangleis a triangle in which two sides are equal in length.

THE ISOSCELES TRIANGLE THEOREM

In an isosceles triangle:

² base angles are equal

² the line joining the apex to the midpoint of the base bisects the vertical

angle and meets the base at right angles.

C ISOSCELES TRIANGLES [4.4]

c°

48° d°

76°

b° ()b°¡-¡5

()b°¡+¡5

a°

4 a° 4 a°

72 °

65 °

d°

a° c°

40 ° b°

120 °b°a°

48 °

84 °

b°

a°

base

base angles

apex

aa

bb

GEOMETRY

PACKAGE

The angles opposite the two equal sides are called the.

The vertex where the two equal sides meet is called the.

base angles

apex

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Y:\HAESE\IGCSE01\IG01_04\100IGCSE01_04.CDR Friday, 12 September 2008 3:19:59 PM PETER