Answer:
person must have to use the concave lens of focal length 3.5 m
Explanation:
If the person can see upto distance of 3.5 m from eye
then in order to see the object at large distance we need to use
[tex]d_o = infinite[/tex]
[tex]d_i = -3.5 m[/tex]
so by lens formula we have
[tex]\frac{1}{d_i} + \frac{1}{d_o} = \frac{1}{f}[/tex]
[tex]\frac{1}{-3.5} + 0 = \frac{1}{f}[/tex]
so we have
f = -3.5 m
so person must have to use the concave lens of focal length 3.5 m