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Therefore, y + x + x = 180°

70° + 2x = 180°
2x = 180° – 70°
2x = 110°

110°
x = = 55°
2

Thus, the measure of the angles of the given triangle is 70°, 55°, and 55°.

Practice Time 8A

1. In ∠ABC, D is the mid-point of BC. Then, A
AM is ..........................
AD is ...........................

Is AM = AD? B M D C
2. Which among them will represent an altitude of the triangle ABC?
A

B L C
3. Can a triangle have three angles whose measures are
(a) 33°, 42°, 115° (b) 45°, 74°, 51° (c) 28°, 59°, 93°?

4. Find the value of the missing angle of the following triangles.
(a) (b) (c) A (d)
x x 3x
30° x 2x
30° x
60° 60° 40°
B C
(e) (f)
2x x

x
x x
5. Find the value of the unknown exterior angle x in the following triangles.

(a) (b) (c) (d)
50° 65° 60°
x
70° x 45° x
x 30° 40° 60°

(e) (f)
50°
x
30°
50° 60°
x

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