# A concave mirror forms a real image at 17.0 cm from the mirror surface along the principal axis. If the corresponding object is at a distance of 36.0 cm, what is the mirror's focal length?

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Dec 16, 2016

#### Answer:

The focal length is $= 11.5 c m$

#### Explanation:

We use the " mirror formula"

$\frac{1}{f} = \frac{1}{d} _ o + \frac{1}{d} _ i$

Object distance ${d}_{o} = 36 c m$

Image distance ${d}_{i} = 17 c m$

So,

$\frac{1}{f} = \frac{1}{36} + \frac{1}{17} = \frac{17 + 36}{17 \cdot 36} = \frac{53}{17 \cdot 36}$

$f = \frac{17 \cdot 36}{53} = 11.5 c m$

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