A) 36 cm
B) 72 cm
C) 18 cm
D) 9 cm
Correct Answer: A
Solution :
[a] \[\frac{1}{3x}+\frac{1}{x}=\frac{1}{f}\]or \[\frac{4}{3x}=\frac{1}{f}\] | ...(i) | |
\[\frac{1}{2(6+x)}+\frac{1}{6+x}=\frac{1}{f}\] | ||
or \[\frac{3}{2(6+x)}=\frac{1}{f}\] | ...(ii) | |
(i) and (ii) gives \[\frac{4}{3x}=\frac{3}{2(6+x)}\] |
\[\therefore \] \[9x=48+8x\] |
\[x=4\text{8 cm}\] |
Shift of screen \[=3x-2(6+x)\]\[=3\times 48-2(6+48)\]\[=3\text{6 cm}\] |
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