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Assertion (A): An equilateral triangle is also an isosceles triangle. Reason (R): An isosceles triangle has at least two equal sides. Which is correct?

Class 7The Triangle and its PropertiesTriangles
  • ABoth A and R are true and R correctly explains A
  • BBoth A and R are true but R does not explain A
  • CA is true but R is false
  • DA is false but R is true

Step-by-Step Solution

An equilateral triangle has all three sides equal, so it certainly has at least two equal sides, making it isosceles. R correctly explains A.
Answer: A) Both A and R are true and R correctly explains A

Key idea: Side-angle relationship

**The longest side of a triangle is opposite the largest angle. The shortest side is opposite the smallest angle.**

In an isosceles triangle, the two equal sides face equal angles. In an equilateral triangle, all sides equal → all angles 60°.

This lets you order sides if you know the angles, or vice versa, even without computing exact values.

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