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Q3   In Fig. 6.44, ABC and DBC are two triangles on the same base BC. If AD intersects BC at O, show that

        \frac{ar (ABC)}{ar ( DBC )} = \frac{AO}{DO}

      

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Let DM and AP be perpendicular on BC.

area\,\,of\,\,triangle=\frac{1}{2}\times base\times perpendicular

\frac{ar(\triangle ABC)}{ar(\triangle BCD)}=\frac{\frac{1}{2}\times BC\times AP}{\frac{1}{2}\times BC\times MD}

In \triangle APO\, and\, \triangle DMO,

\angle APO=\angle DMO           (Each 90 \degree)

\angle AOP=\angle MOD           (Vertically opposite angles)

\triangle APO\, \sim \, \triangle DMO,       (AA similarity)

\frac{AP}{DM}=\frac{AO}{DO}    

Since 

         \frac{ar(\triangle ABC)}{ar(\triangle BCD)}=\frac{\frac{1}{2}\times BC\times AP}{\frac{1}{2}\times BC\times MD}

\Rightarrow \frac{ar(\triangle ABC)}{ar(\triangle BCD)}=\frac{AP}{ MD}=\frac{AO}{DO}

 

 

 

 

 

 

 

 

 

 

 

Posted by

seema garhwal

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