16Hit1600
Geometry and TrigonometryEasyAngles on a straight line

Geometry and Trigonometry practice question

Two straight lines intersect at a point. One of the four angles formed measures 35°. What is the measure of an angle that is adjacent to it along one of the lines?

  1. A. 145°Correct
  2. B. 35°
  3. C. 55°
  4. D. 325°

Answer: A. 145°

Two angles that sit next to each other along a straight line are supplementary — they add to 180°. So the adjacent angle measures 180° − 35° = 145°.

Why the other answers are wrong

B. 35°
35° is the measure of the angle OPPOSITE the given one (vertical angles are equal). The question asks for the angle next to it along a line, which together with 35° makes a straight 180°.
C. 55°
55° is 90° − 35°, treating the two angles as complementary. Angles along a straight line add to 180°, not 90°.
D. 325°
325° is 360° − 35°, the rest of the full turn around the point. The two angles that share one straight line add to 180°.

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