IXL | Find missing angles in special triangles

One angle of a right triangle measures 85°. What is the measure of the other acute angle?

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question

One angle of a right triangle measures 80°. What is the measure of the other acute angle?

key idea

The measures of the angles of a triangle add up to 180°.

solution

A right triangle has a 90° angle, so you know that two of the angles are 90° and 80°.

Find the missing angle. Set the sum of the angle measures equal to 180° and solve.

90° + 80° + n

180°

Add

170° + n

180°

Add

Subtract 170° from both sides

180° − 170°

Subtract 170° from both sides

Simplify

10°

Simplify

So, the other acute angle measures 10°.

Looking for more? Try these:

Lesson: Types of triangles

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Teacher tools

Work it out

Not feeling ready yet? These can help:

DD.2Measure and classify angles

EE.7Find missing angles in triangles

G.8Complete the addition sentence: up to three digits

Lesson: Types of triangles

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