7-2: exterior angle theorem. e xterior a ngle : an angle of a triangle that forms a linear pair with...

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7-2: Exterior Angle Theorem

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Page 1: 7-2: Exterior Angle Theorem. E XTERIOR A NGLE : An angle of a triangle that forms a linear pair with one of the angles of the triangle. R EMOTE I NTERIOR

7-2: Exterior Angle Theorem

Page 2: 7-2: Exterior Angle Theorem. E XTERIOR A NGLE : An angle of a triangle that forms a linear pair with one of the angles of the triangle. R EMOTE I NTERIOR

7-2: Exterior Angle Theorem

EXTERIOR ANGLE: An angle of a triangle that forms a linear pair with one of the angles of the triangle.

REMOTE INTERIOR ANGLES: The angles that do not form a linear pair with the exterior angle.

Exterior AngleRemoteInteriorAngle

Page 3: 7-2: Exterior Angle Theorem. E XTERIOR A NGLE : An angle of a triangle that forms a linear pair with one of the angles of the triangle. R EMOTE I NTERIOR

7-2: Exterior Angle Theorem

Identify each exterior angle.Then, identify the remote interior angles

Note that each exterior angle at a vertex share the same interior angles

Exterior Angle Remote Interior Angles

4 2 & 3

5 1 & 3

6 1 & 3

7 1 & 2

8 1 & 2

9 2 & 3

Page 4: 7-2: Exterior Angle Theorem. E XTERIOR A NGLE : An angle of a triangle that forms a linear pair with one of the angles of the triangle. R EMOTE I NTERIOR

7-2: Exterior Angle Theorem

Theorem 7-3 (EXTERIOR ANGLE THEOREM): The measure of an exterior angle of a triangle is equal to the sum of its two remote interior angles. 4 = 1 + 2

Discuss Proof 41

2

3

Page 5: 7-2: Exterior Angle Theorem. E XTERIOR A NGLE : An angle of a triangle that forms a linear pair with one of the angles of the triangle. R EMOTE I NTERIOR

7-2: Exterior Angle Theorem

If m2 = 38 and m4 = 134, what is m5? 4 = 2 + 5 134 = 38 + 5 96 = 5

If m2 = x + 17, m3 = 2x, and m6 = 101, find the value of x. 6 = 2 + 3 101 = x + 17 + 2x 101 = 3x + 17 84 = 3x 28 = x

Page 6: 7-2: Exterior Angle Theorem. E XTERIOR A NGLE : An angle of a triangle that forms a linear pair with one of the angles of the triangle. R EMOTE I NTERIOR

7-2: Exterior Angle Theorem

Your Turn What is 1 if m3 = 46 and m5 = 96?

142 If m2 = 3x, m3 = x + 34, and m6 = 98, find the

value of x. Then, find m3. x = 16 m3 = 50

Page 7: 7-2: Exterior Angle Theorem. E XTERIOR A NGLE : An angle of a triangle that forms a linear pair with one of the angles of the triangle. R EMOTE I NTERIOR

7-2: Exterior Angle Theorem

Two “common sense” theorems are derived from the Exterior Angle Theorem. Theorem 7-4: The measure of an exterior angle of a

triangle is greater than the measure of either of its two remote interior angles.

Theorem 7-5: If a triangle has one right angle, then the other two angles must be acute.

Page 8: 7-2: Exterior Angle Theorem. E XTERIOR A NGLE : An angle of a triangle that forms a linear pair with one of the angles of the triangle. R EMOTE I NTERIOR

7-2: Exterior Angle Theorem

Assignment Worksheet #7-2