\[\boxed{\mathbf{1325.еуроки - ответы\ на\ пятёрку}}\]
\[Решение.\]
\[AE \bullet EB =\]
\[= DE \bullet CE\ (по\ свойству\ хорд).\]
\[\textbf{а)}\ AE = 5;BE = 2;CE = 2,5:\]
\[5 \bullet 2 = DE \bullet 2,5\]
\[10 = 2,5 \bullet DE\]
\[DE = \frac{10}{2,5} = 4.\]
\[\textbf{б)}\ AE = 16;BE = 9;CE = ED:\]
\[16 \bullet 9 = DE \bullet DE\]
\[DE^{2} = 16 \bullet 9\]
\[DE = \sqrt{16 \bullet 9} = 4 \bullet 3 = 12.\]
\[\textbf{в)}\ AE = 0,2;BE = 0,5;CE = 0,4:\]
\[0,2 \bullet 0,5 = DE \bullet 0,4\]
\[0,1 = DE \bullet 0,4\]
\[DE = \frac{0,1}{0,4} = \frac{1}{4} = 0,25.\]
\[Ответ:а)\ 4;б)\ 12;в)\ 0,25.\]