[tex]BD = \frac{30}{100}DC=\frac {3}{10}DC \\ \\
BD+DC = BC \\ \\ \frac{3}{10}DC+DC=26 hm \\ \\ \frac{13DC}{10}=26 \\ \\DC = \frac{26*10}{13}\\ \\
DC=20 (hm) =\ \textgreater \ BD= 6(hm)
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tr. ABC, m(A)=90; m(D)=90 =\ \textgreater \ AD^{2}=BD*DC=\ \textgreater \ \\
AD= \sqrt{20*6} =\sqrt{4*5*6}=2\sqrt{30} (hm)[/tex]
