The image produced by an object is –10.0 cm from a concave mirror that has a focal length of 5.0 cm. the distance of the object from the mirror, rounded to the nearest whole centimeter, is __cm.

Given:
Focal length: 5.0 cm
image produced: -10.0 cm

mirror equation:   1/di + 1/do = 1/f

Look for the actual distance of the object from the mirror. Solve for do.

1/do + 1/(-10) = 1/5
1/do = 1/5 + 1/10
1/do = (1/5 * 2/2) + (1/10 * 1/1)
1/do = 2/10 + 1/10
1/do = 3/10
10 = 3do
10/3 = do
3.33 = do

The distance of the object from the mirror, rounded to the nearest centimeter is 3 cm.

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