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Euclid's fourth postulate states that ____.

Class 9Introduction to Euclid's GeometryGeometry — Foundations
  • AAll right angles are equal to one another
  • BAll straight lines are equal
  • CAll circles are equal
  • DAll triangles are congruent

Step-by-Step Solution

Postulate 4 asserts that all right angles equal one another, giving a fixed standard of angle measure.
Answer: A) All right angles are equal to one another

Key idea: The five postulates of Euclid

**Postulate 1**: A straight line may be drawn from any one point to any other point.

**Postulate 2**: A terminated line (segment) can be produced indefinitely (extended).

**Postulate 3**: A circle can be drawn with any centre and any radius.

**Postulate 4**: All right angles are equal to one another.

**Postulate 5** (the famous one): If a straight line falling on two straight lines makes the interior angles on the same side together less than two right angles (180°), then the two lines, if produced indefinitely, meet on that side on which the angles are less than two right angles.

These 5 statements are the seeds. Everything else in classical geometry grows from them.

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