Easy Angles 2

Geometry Level 3

In A B C \triangle{ABC} , A \angle{A} is 3 0 30^\circ and B \angle{B} is 8 0 80^\circ . What is the measure of the complement of C \angle{C} in degrees?


The answer is 20.

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3 solutions

Siva M.
Aug 6, 2014

Let the measure of C \angle{C} be x x . We know that the sum of a triangle's angles is 18 0 180^\circ . We also know that the first two angles sum up to 11 0 110^\circ . From this, the measure of C \angle{C} is 18 0 11 0 = 7 0 180^\circ-110^\circ=70^\circ . The complement of an angle is 90 z 90-z , where z z is the measure of the angle in degrees. Thus, the complement of C \angle{C} is 9 0 7 0 = 2 0 90^\circ-70^\circ=\boxed{20^\circ} .

"The compliment" is not frequently used.

Mark Derry - 4 years, 6 months ago

Indeed but you learn something new every day

Ben Bower - 4 years, 4 months ago

How is this a "Level 3" problem? Isn't some levelheadedness required here?

Ajit Athle - 2 years, 10 months ago
Mahdi Raza
May 13, 2020

\[\begin{align} \angle A + \angle B + \angle C &= 180^{\circ} \\ (30^{\circ}) + (80^{\circ}) + \angle C &= 180^{\circ} \\ \angle C &= 70^{\circ} \implies \color{Blue}{[90 - 70 = \boxed{20}]}

\end{align}\]

A C B = 180 80 30 = 70 \angle ACB=180-80-30=70

The sum of complimentary angles is 9 0 90^\circ . So the complement of A C B \angle ACB is 90 70 = 90-70= 20 \boxed{20}

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