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ANGLES IN TRIANGLES LESSON 16(3)

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TYPES OF TRIANGLES ACUTE TRIANGLE - a traingle with three acute angles. RIGHT TRIANGLE - a triangle with a right angle. ( 90o angle) OBTUSE TRIANGLE - a triangle with an obtuse angle. SCALENE TRIANGLE - no sides are the same, no angles are the same. ISOSCELES TRIANGLE - two sides are the same, base angles are the same. EQUILATERAL TRIANGLE - all sides are the same, all angles are the same. ( 60o )

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**SUM OF ANGLES IN TRIANGLES**

The sum of the angles in a triangle is 180o. PROOF: Using Parallel Lines. 1 = 4 and 3 = 5 But 1 + 2 + 3 = 180o If 1 is replaced with 4 and 3 with 5, then 4 + 2 + 5 = 180o (Z pattern) (straight angle)

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**EXTERNAL ANGLE OF A TRIANGLE**

An exterior (or external) angle is the angle between one side of a triangle and the extension of an adjacent side External angle

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**EXTERNAL ANGLE OF A TRIANGLE**

PROPERTIES: An exterior angle of a triangle is equal to the sum of the opposite interior angles. In the figure below the exterior angle 1 is equal to the sum of the angles 3 and 4 1 = 3 + 4 External angle

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**Write an equation for the exterior angle of the triangle.**

YOU TRY

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**SOLUTION Exterior angle xo = zo + wo**

Write an equation for the exterior angle of the triangle. SOLUTION Exterior angle xo = zo + wo

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**Calculate the measures of the unknown angles. State how you know.**

YOU TRY

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**SOLUTION t = 30o ( sum of triangle ) s = 50o ( sum of triangle )**

Calculate the measures of the unknown angles. State how you know. SOLUTION u = 60o ( supplement to 120o ) t = 30o ( sum of triangle ) s = 50o ( sum of triangle ) r = 130o ( supplement to so )

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**Class work Check solutions to Lesson 16(2)**

Copy down notes and examples from this lesson. Do Lesson 16(3) worksheet

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