A radionuclide  $A_1$ with decay constant  ${\lambda }_1$ transforms into a radionuclide $A_2$ with decay constant  ${\lambda }_2$. Assuming that at the initial moment the preparation contained only the radionuclide $A_1$. Find the time interval after which the activity of radioactivity $A_2$  reaches the maximum value. If $t=\frac{2\mathcal{l}n({\lambda }_1/{\lambda }_2)}{n({\lambda }_1-{\lambda }_2)}$ find n……