Same-Side Interior Angles
Same-side interior angles are the pair of angles that lie between two parallel lines and on the same side of a transversal. For parallel lines, these angles are supplementary, so their measures add to 180°.
Method
- Identify the two interior angles in the diagram.
- Write an equation showing that their sum is 180°.
- Example form:
angle 1 + angle 2 = 180
- Substitute the given expressions or values.
- Solve for the unknown.
- Find each angle measure if needed by plugging the value back in.
What to watch for
- Make sure the angles are both inside the parallel lines.
- They must be on the same side of the transversal.
- If the problem gives expressions, simplify carefully before or after solving.
Check your work
Add the two angle measures. If the lines are parallel, the total should be 180°. If your answer is not 180°, recheck the algebra and the angle pair you chose.