An equilateral triangle ABC has perimeter 24 cm. The median from A meets BC at D. Find BD in cm.

Class 7The Triangle and its PropertiesTriangles

Step-by-Step Solution

Each side is 24 ÷ 3 = 8 cm, so BC = 8 cm. A median ends at the midpoint of the opposite side, so BD = 8 ÷ 2 = 4 cm. Trap: answering 8 (the whole side BC) or 12 (half the perimeter) instead of halving the single side the median actually meets.

Answer: D) 4

Key idea: Angle sum property

**The three interior angles of any triangle sum to 180°.**

This is true for every triangle — equilateral, isosceles, scalene, right, acute, or obtuse. Use it to find a missing angle when you know the other two: third angle = 180° − (first) − (second).

Special cases:
- Equilateral: all angles equal → each is 60°.
- Right triangle: one is 90°, so the other two sum to 90° (they are complementary).

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