NCERT Class 7 Mathematics

THE TRIANGLE AND ITS PROPERTIES 119 Find the value of the unknown interior angle x in the following figures: 6.5 ANGLE SUM PRO ...

120 MATHEMATICS Arrange them as in Fig 6.15. What do you observe about ∠1 + ∠2 + ∠3? (Do you also see the ‘exterior angle proper ...

THE TRIANGLE AND ITS PROPERTIES 121 Given ∠1,∠2,∠3 are angles of ΔABC (Fig 6.17). ∠4 is the exterior angle when BC is extended t ...

122 MATHEMATICS Two angles of a triangle are 30º and 80º. Find the third angle. One of the angles of a triangle is 80º and the ...

THE TRIANGLE AND ITS PROPERTIES 123 A triangle in which two sides are of equal lengths is called an isosceles triangle. Fig 6.20 ...

124 MATHEMATICS Find angles x and y in each figure. 6.7 SUM OF THE LENGTHS OF TWO SIDES OF A TRIANGLE Mark three non-collinea ...

THE TRIANGLE AND ITS PROPERTIES 125 Draw any three triangles, say ΔABC,ΔPQR and ΔXYZ in your notebook (Fig 6.22). (i) (ii) (ii ...

126 MATHEMATICS EXAMPLE 3 Is there a triangle whose sides have lengths 10.2 cm, 5.8 cm and 4.5 cm? SOLUTION Suppose such a trian ...

THE TRIANGLE AND ITS PROPERTIES 127 The lengths of two sides of a triangle are 12 cm and 15 cm. Between what two measures shoul ...

128 MATHEMATICS The squares are identical; the eight triangles inserted are also identical. Hence the uncovered area of square A ...

THE TRIANGLE AND ITS PROPERTIES 129 Repeat the above activity with squares whose sides have lengths 4 cm, 5 cm and 7 cm. You ge ...

130 MATHEMATICS EXERCISE 6.5 PQR is a triangle right angled at P. If PQ 10 cm and PR 24 cm, find QR. ABC is a triangle right an ...

THE TRIANGLE AND ITS PROPERTIES 131 THINK, DISCUSS AND WRITE Which is the longest side in the triangle PQR right angled at P? W ...

132 MATHEMATICS This property is useful to know if it is possible to draw a triangle when the lengths of the three sides are kno ...

7.1 INTRODUCTION You are now ready to learn a very important geometrical idea, Congruence. In particular, you will study a lot a ...

134 MATHEMATICS The relation of two objects being congruent is called congruence. For the present, we will deal with plane figur ...

CONGRUENCE OF TRIANGLES 135 In view of the above fact, when two line segments are congruent, we sometimes just say that the line ...

136 MATHEMATICS As in the case of line segments, congruency of angles entirely depends on the equality of their measures. So, to ...

CONGRUENCE OF TRIANGLES 137 EXAMPLE 1 ΔABC and ΔPQR are congruent under the correspondence: ABC↔RQP Write the parts of ΔABC that ...

138 MATHEMATICS 7.6 CRITERIA FOR CONGRUENCE OF TRIANGLES We make use of triangular structures and patterns frequently in day-to- ...