LA5 marksYear: 2025HardCBSE Class 10
trianglesBPTbasic-proportionality-theoremproof
Question
Prove that a line drawn parallel to one side of a triangle to intersect the other two sides in distinct points divides the other two sides in the same ratio. Hence, in the figure given below, prove that MBAM=NDAN where LM∥CB and LN∥CD.

Solution
1
Correct figure, given, to prove and construction.
+1.5 marks2
Correct proof of BPT (Basic Proportionality Theorem).
+1.5 marks3
In △ABC, LM∥CB:
MBAM=LCAL ... (1)
+1 mark4
In △ADC, LN∥CD:
NDAN=LCAL ... (2)
From (1) and (2), we have
MBAM=NDAN
+1 mark