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Constructions

Question
CBSEENMA9002889

 ΔABC and ΔABD are two triangles on the same base AB. If line segment CD is bisected by AB at O, show that ar (ΔABC) = ar (ΔABD).

ar left parenthesis quad. space ABCD right parenthesis equals 1 half BD. left parenthesis AM plus CN right parenthesis.

Solution

Given: BD is one of the diagonals of a quadrilateral ABCD. AM and CN are perpendiculars from A and C respectively on BD.

To Prove: ar(quad. ABCD)
equals 1 half BD. left parenthesis AM plus CN right parenthesis
Proof: ar(quad ABCD)

negative ar left parenthesis increment ABD right parenthesis plus ar left parenthesis increment BCD right parenthesis
equals space fraction numerator BD. AM over denominator 2 end fraction plus fraction numerator BD. CN over denominator 2 end fraction
because  Area of a triangle = 1 half x Base X Corresponding altitude
equals 1 half BD left parenthesis AM plus CN right parenthesis