Angle Problem Examples

Angle problems will mostly show up as triangles, but you should be prepared for any polygon.

An example:

Since we know two of the angles, we can find the third.  (90+33=123).  The total degrees is 180, so (180–123=57^circ).

There is another rule that helps when dealing with triangles: across from equal sides are equal angles! This helps to explain why all of the angles in an equilateral triangle are congruent, because they’re all across from equal sides.

Now, let’s take an example where you put all three of these to use.

In the figure above, line segments AB and CD intersect at point E.  What is the value of ?

A) 60°
B) 65°
C) 70°
D) 75°

You can use the supplement of 130° to find the second angle of the triangle, then use the interior angles of a triangle, then opposite angles, and finally interior angles of an (isosceles) triangle.