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It is given that,

Focal length

f=−20cm

hi=3ho

The image is three times the size of the object. So there are two cases.

Case 1. For real image

m=−vu=−3

v=3u

Using mirror’s formula

1f=1v+1u

1−20=13u+1u

u=−803cm

Case 2. For virtual image

m=−vu=+3

v=−3u

Again using mirror’s formula

1−20=1−3u+1u

u=−403cm

The possible values of u are −803cmand−403cm.

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