How to Determine a Right Triangle

Using a Protractor

Align a protractor on one side of a triangle.

Measure the angle by relating to an adjacent segment.

Check the measurement to see if it is 90º. If it is 90º, it is a right triangle. Remember that you just need one right angle to have right triangle. You can check one or two more times to be accurate.

Repeat this for the remaining angles.

Using an Edge

Find an object that for sure has a 90º angle. Some objects include: Notebook paper Sticky notes Rulers (common and standard) Cubic object

Place the corner/vertex of the object on an angle made by two intersecting segments. One of the straightedges has to align to one of the segments.

Check to see if the other segment aligns to the other straightedge. If it does, then it is most likely that the angle measures 90º, it is a right angle, and the triangle is right. During your homework or tests/quizzes, feel free to call it a right angle even if there is a minuscule difference. It is most likely, even cliche, that work from school will not be that specific.

Repeat for the remaining angles.

Using Other Angles to Find The Remaining Angle

Determine the other 2 angles.

Add the angles.

Subtract the sum of the angles' measures by 180º. This will give you the measure of the remaining angle.

Check to see if the angle measures 90º. If it is, it is a right angle and the triangle is also right.

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