Which statement is true about an angle with a measure of 180 degrees?

• A. Acute angle
• B. Right angle
• C. Obtuse angle
• D. Straight angle

Answer: (D)

Angles are classified by their measures. An angle that measures 180 degrees forms a straight line, with the two rays pointing in opposite directions from a common endpoint. That is a straight angle.

Acute angles are less than 90 degrees, so they look like small openings. A right angle is exactly 90 degrees, like a perfect corner. An obtuse angle is greater than 90 degrees but less than 180, opening wider than a right angle but not all the way straight. Since 180 degrees sits exactly on the straight line, it fits the straight angle description rather than acute, right, or obtuse.