The correct answer is: [A]: "69° " .
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m∠1 = 69° .
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Explanation:
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180 - (39 + 30) = 180 - 69 = 111. This is the measurement of the third angle in the triangle. Note that all angles in a triangle add up to 180° . All triangles have 3 (three) sides and 3 (three) angles.
To find m∠1 :
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The only single angle that exists that is supplementary to ∠1 is 69.
So: m∠1 = 180 - 111 = 69 . (Note: since all angles on a straight line are supplementary angles; and supplementary angles add up to 180° .
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The answer is: 69° .
m∠1 = 69° .
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