Use a protractor to measure one of the angles. Line up the bottom edge of the protractor with one of the lines and measure the angle at which the other line intersects it. The center point, or origin, on the protractor must be lined up with the vertex of the angle to get a correct measurement.
Calculate the measure of the angle opposite the one you measured in Step 1 by setting it equal to the measured angle.
Subtract the value of each measured angle from 180 degrees (or from pi if you are using radians) to find the measure of the two angles adjacent to the measured angle.