The focal length of a concave lens is expressed as,
[tex]\frac{1}{f}=\frac{1}{u}+\frac{1}{v}[/tex]Here, f is the focal length, u is the distance of object and v is the distance of image.
Plug in the known values,
[tex]\begin{gathered} \frac{1}{18\text{ cm}}=\frac{1}{10.0\text{ cm}}+\frac{1}{v} \\ \frac{1}{v}=\frac{1}{18\text{ cm}}-\frac{1}{10.0\text{ cm}} \\ v=\frac{(18\text{ cm)(10.0 cm)}}{10.0\text{ cm-18 cm}} \\ =-22.5\text{ cm} \end{gathered}[/tex]Thus, the distance of image is -22.5 cm where negative sign indicates that the image will be at the same side of object.
