Page 159 - New Medley 5 Semester 2

What do you conclude?

Property 1: The sum of three angles of a triangle is always 180°.

Property 2: The sum of any two sides of a triangle is greater than the

third side.

Example 1: Can a triangle have the angles of the following

measures?

(a) 40°, 30°, 50° (b) 60°, 70°, 80° (c) 60°, 60°, 60°

Solution: (a) As 40° + 30° + 50° = 120° < 180°

So, the triangle cannot be formed with these angles.

(b) As 60° + 70° + 80° = 210° > 180°

So, the triangle cannot be formed with these angles.

(c) As 60° + 60° + 60° = 180°

Here, the sum of three angles is 180°, so the triangle
can be formed with these angles.

Example 2: The measures of two angles of a triangle are 25° and
75°. Find the measure of third angle.

Solution: Given, the two angles are 25° and 75°.

Sum of these angles = 25° + 75° = 100°

\ The third angle of the triangle = 180° – 100° = 80°

Example 3: Does a triangle have the sides of measures 4 cm, 8 cm

and 3 cm?

Solution: Since 4 cm + 8 cm = 12 cm > 3 cm and 8 cm + 3 cm =

11 cm > 4 cm

But, 4 cm + 3 cm = 7 cm < 8 cm

Thus, the triangle cannot have the given measures of

sides.

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