2025 · Basic · Set 1 · Part 3·Q34·5 marks

Triangles

Question

State the converse of "Basic Proportionality Theorem" and use it to prove the following:

Line segment joining mid-points of any two sides of a triangle is parallel to the third side.

Approach

Converse of BPT: If a line divides two sides of a triangle in the same ratio, then it is parallel to the third side. Given D and E are midpoints of AB and AC, so AD/DB = 1 and AE/EC = 1. Since the ratios are equal, by converse of BPT, DE is parallel to BC.

Step-by-step working

  1. 1

    Statement of converse BPT

    1 mark
  2. 2

    Given, To prove, correct figure

    1 mark
  3. 3

    D is midpoint of AB AD/DB = 1

    1 mark
  4. 4

    E is midpoint of AC AE/EC = 1 AD/DB = AE/EC

    1 mark
  5. 5

    By converse of BPT, DE BC

    1 mark

Concepts used

basic proportionality theoremconversemidpoint theoremparallel lines

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