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\(\triangle\)ABC এর \(\angle\)A=90° এবং AD\(\bot\)BC
\(\therefore \cfrac{1}{2}\times\)AB \(\times\)AC \(=\cfrac{1}{2}\times \) BC\(\times\) AD
বা, \(\cfrac{1}{2}\times 20 \times 15 =\cfrac{1}{2}\times 25 \times\) AD
বা, AD=\(\cfrac{\cancel{20}4\times \cancel{15}3}{\cancel{25}\cancel5}=12\)

\(\therefore \) AD = 12 cm