In the adjoining figure,the point D divides the side BC of △ ABC in the ratio m:n.Prove that (△ ABD):ar(△ ADC)=m:n.
ar (△ ABD) = ½ x B x H
= ½ x BD x AE
ar(△ ADC) = ½ x B x H
= ½ x CD x AE
Now, their ratio :
½ x BD x AE/1/2 x CD x AE = BD/CD
Therefore BD/CD = BD : CD i.e m:n