Question

This triangle has an exterior angle labeled
. All of the interior angles are labeled correctly.

The interior angles of a triangle are 80 degrees, 60 degrees and 40 degrees. An exterior angle adjacent to an interior angle of 40 degrees is labeled angle A.

Which statement about the exterior angle is correct?

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A
.

It is 140 degrees
because it is supplementary to 40 degrees
.

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B.

It is
50 degrees because it is complementary to 40 degrees
.

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C.

It is 60 degrees
because 60 degrees + 40 degrees = 100 degrees
.

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D.

It is 120 degrees
because 40 degrees + 80 degrees = 120 degrees
.

Answer 1

A. It is 140 degrees — an exterior angle is supplementary to the adjacent interior angle (180 − 40 = 140) and equals the sum of the two remote interior angles (80 + 60 = 140).