Determine the missing angle.

Solution:

• The image shows intersecting lines. Angles that are opposite each other at an intersection are called vertical angles, and they are equal.
• The angle marked 70 degrees and the angle directly opposite it are vertical angles, so that opposite angle is also 70 degrees.
• Angles that lie on a straight line and add up to 180 degrees are called supplementary angles.
• The angle marked 65 degrees and the angle adjacent to it on the straight line form a straight angle. Therefore, the adjacent angle is 180 - 65 = 115 degrees.
• The angle marked with a question mark and the 65-degree angle are vertical angles.
• Therefore, the missing angle is equal to 65 degrees.

Answer: 65°