[tex]1. \beta=\frac{x_2}{x_1}=>x_2=\beta x_1 =1,5*(-20)=-30 cm\\\frac{1}{x_2}- \frac{1}{x_1}= \frac{1}{f}<=>\frac{1}{-30}+\frac{1}{20}=\frac{1}{f}<=>\frac{1}{f}=\frac{-20+30}{600}=>f=60 cm=>f=60 cm\\ \\2.\frac{1}{x_2}- \frac{1}{x_1}= \frac{1}{f}=>\frac{1}{x_2}= \frac{1}{f}+ \frac{1}{x_1}=\frac{1}{1} - \frac{1}{3}=\frac{2}{3} =>x_2=\frac{3}{2} m\\ \beta=-\frac{x_2}{x_1}=-\frac{\frac{3}{2} }{-3}=0,5=>\beta= 0,5\\\\[/tex]
[tex]3. 13\frac{1}{2}=\frac{13*2+1}{2}=\frac{27}{2}= 13,5\\ C= 13\frac{1}{2}=13,5\delta\\C=\frac{1}{f}=>f=\frac{1}{C}=\frac{1}{13,5}= 0,074 m=7,4 cm\\\frac{1}{x_2}-\frac{1}{x_1}=\frac{1}{f}<=>-\frac{1}{15}-\frac{1}{7,4}=\frac{1}{x_1}<=> -\frac{22,4}{111} = \frac{1}{x_1}=>x_1=-4,95 cm\\\\[/tex]
