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How do I know what the measure is of the third angle?

How do I know what the measure is of the third angle?-example-1
User RafaSashi
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1 Answer

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The sum of the inner angles of any triangle is always 180º

So if for example, you have a triangle with angles ∠1, ∠2 and ∠3 and you add them, the result must be 180º:


\angle1+\angle2+\angle3=180º

This is useful when you know the measure only two inner angles.

To calculate the measure of the third one you just have to subtract the known angles to 180º:


\begin{gathered} \angle1+\angle2+\angle3=180º \\ \angle3=180º-(\angle1+\angle2) \end{gathered}

In this exercise, you have the angles

∠1= 23º

∠2= 98º

To determine the measure of the third angle you have to proceed as follows:


\begin{gathered} 23º+98º+\angle3=180º \\ 121º+\angle3=180º \\ \angle3=180º-121º \\ \angle3=59º \end{gathered}

The third angle measures 59º

User NorthIsUp
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