x1=-4f
x1=-4×12
x1=-48cm
[tex] \frac{1}{x2} - \frac{1}{x1} = \frac{1}{f} [/tex]
[tex] \frac{1}{x2} + \frac{1}{48} = \frac{1}{12} [/tex]
[tex] \frac{48 + x2}{48 \times x2} = \frac{1}{12} [/tex]
12(48+x2)=48x2
576+12x2=48x2
576=36x2
x2=16 cm
mairea liniara beta= x2/x1
16/-48 = -1/3 => imaginea este reala
imaginea se afla la 16 cm de lentila