[tex]\text{Daca lentilele sunt alipita,atunci putem considera ca tot sistemul }\\
\text{formeaza o singura lentila,avand convergenta:} \\
C=C_1+C_2\\
\dfrac{1}{f}=\dfrac{1}{f_1}+\dfrac{1}{f_2}\\
\dfrac{1}{f}=\dfrac{f_2+f_1}{f_1\cdot f_2}\\
f=\dfrac{f_1\cdot f_2}{f_1+f_2},
\text{ceea ce trebuia sa sti demonstram.}\\ \text{ In fine ,daca continuam calculele:}\\
f=\dfrac{8\cdot 2}{8+2}=\dfrac{16}{10}=1,6\ cm
[/tex]
