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Geometry and TrigonometryVery hardAngles formed by parallel lines

Geometry and Trigonometry practice question

Two parallel lines are cut by a transversal. One of the eight angles measures 47°. Which of the following is NOT a possible measure of another one of the eight angles?

  1. A. 47°
  2. B. 133°
  3. C. 43°Correct
  4. D. 180° − 47°

Answer: C. 43°

With parallel lines and a transversal, every angle equals either 47° (corresponding/vertical/alternate) or its supplement 133°. 43° never appears — it's the complement, a tempting-but-wrong trap. Note D equals 133°.

Why the other answers are wrong

A. 47°
47° does appear — the vertical, corresponding, and alternate angles to the given one all measure 47°.
B. 133°
133° is possible: it's the supplement of 47°, and every angle in the figure is either 47° or 133°.
D. 180° − 47°
180° − 47° is just 133°, the supplement, which does appear among the eight angles.

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