Answer:
[tex]20[/tex] cm
Explanation:
[tex]d_{o}[/tex] = distance of the object = ?
[tex]f[/tex] = focal length of the convex mirror = - 20 cm
[tex]d_{i}[/tex] = distance of the image = - 10 cm
Using the lens equation
[tex]\frac{1}{d_{o}} + \frac{1}{d_{i}} = \frac{1}{f}[/tex]
[tex]\frac{1}{d_{o}} + \frac{- 1}{10} = \frac{- 1}{20}[/tex]
[tex]d_{o} = 20[/tex] cm
