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Which triangle type is described as having all three sides of different lengths?

Class 7The Triangle and its PropertiesTriangles
  • AScalene
  • BEquilateral
  • CIsosceles
  • DRight

Step-by-Step Solution

A scalene triangle has all three sides different lengths (and all three angles different). Equilateral has all sides equal; isosceles has two equal; 'right' refers to an angle, not sides.
Answer: A) Scalene

Key idea: Triangle inequality

**The sum of any two sides of a triangle is greater than the third side.**

So a triangle with sides 3, 4, 5 works (3+4>5, 3+5>4, 4+5>3). But sides 1, 2, 5 do NOT form a triangle — 1 + 2 = 3 is less than 5, so the two short sides can't reach across.

Use this to test whether three given lengths can be a triangle, or to bound a missing side: if two sides are 5 and 8, the third must be greater than 8 − 5 = 3 AND less than 8 + 5 = 13.

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