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Can two right angles be supplementary to each other?

Class 7Lines and AnglesLines and Angles
  • ANo — supplementary angles must always be one acute and one obtuse.
  • BNo — two right angles are complementary, not supplementary.
  • COnly if the two right angles are adjacent to each other.
  • DYes — 90° + 90° = 180°.

Step-by-Step Solution

Supplementary means the two measures sum to 180°, and 90 + 90 = 180, so two right angles are indeed supplementary. Trap: the first option adds a condition that does not exist — the only requirement is the sum. The second swaps the words: complementary means a sum of 90°, and 90 + 90 is not 90. Adjacency is never required either.
Answer: D) Yes — 90° + 90° = 180°.

Key idea: Parallel lines and a transversal

When a transversal crosses two **parallel** lines, eight angles form (four at each intersection). They come in special pairs:

- **Corresponding angles**: same position at each intersection (e.g. both top-left). **Equal**.
- **Alternate interior angles**: between the parallel lines, on opposite sides of the transversal. **Equal**.
- **Alternate exterior angles**: outside the parallel lines, on opposite sides of the transversal. **Equal**.
- **Co-interior (same-side interior) angles**: between the parallel lines, on the same side of the transversal. **Supplementary** (sum to 180°).

These are the rules you'll use most. Sketch the figure and label what you know — the rest follows quickly.

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