Find the measure of the angle
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Find the measure of the angle
Recall that the sum of angles in a triangle equals 180 degrees.
Therefore, we will use the following formula:
Now let's insert the known data:
We will simplify the expression and keep the appropriate sign:
80
Can a triangle have a right angle?
This is an isosceles triangle - it has two equal sides, which means it also has two equal angles. The diagram shows both base angles are 50°.
No! The angle sum property () is the fundamental rule for all triangles. It's the only way to find missing angles when you know the other angles.
You probably only used one 50° angle instead of both! Remember: , not . Always count all given angles.
Look at the diagram carefully! The angle marked with the Greek letter α (alpha) is at the top vertex of the triangle, opposite to the longest side.
Test it! If α = 90°, then 90 + 50 + 50 = 190°, which is too much for a triangle. If α = 110°, then 110 + 50 + 50 = 210°, which is way too much!
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