A right triangle has one angle that measures 77°. What is the measurement for the missing angle?

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Answer 1 · 2018-05-16T18:24:17

The missing angle is $13^@$

Let $angleB$ be the missing angle.

Let $angleA$ be the angle that measures $77^@$

Let $angle C$ the right angle that measures $90^@$

The following is true of all triangles:

$angleA+angleB+angleC = 180^@$

Express the above equation as $angleB$ in terms of the other angles:

$angleB = 180^@-angleA-angleC$

Substitute the values for $angle A$ and $angleC$

$angleB = 180^@-77^@-90^@$

$angleB = 13^@$