Find any right angles. Right angles are denoted in geometry problems by a square in the lower corner of the angle. Right angles are 90 degrees.
Find all the unknown angle. If you know two of the interior angles in a triangle, subtract them from 180 because the angles of a triangle always add to 180 degrees. For example, if you see a triangle with one angle labeled as 56 degrees and another one labeled as 78 degrees, the final angle has to be 46 degrees.
Look for vertical angles. When two lines intersect, they form two pairs of angles opposite one another. The adjacent angles will always add to 180 degrees, and the opposite, or vertical, angles will be equal. For example, if one line intersects another line at a 45-degree angle, it forms a pair of 45-degree angles opposite one another and a pair of 135-degree angles opposite one another.
Look for parallel lines intersected by the same line. The measurements will be equal for the corresponding sets of angles.