The lens equation (1/p) + (1/q) + = (1/f) relates the distance p of an object from a lens, the distance q of the image of the object from the lens, and the focal length f of the lens. What is this distance of an object from a lens if the image of the object is 7 centimeters from the lens and the focal length of the lens is 3 centimeters?

If you could do that, then I applaud you.
I've been trying to figure it out but I'm so confused.
Please show me how you did it step by step
Thank you to anyone who tries!

2. Originally Posted by gnarlycarly227
The lens equation (1/p) + (1/q) + = (1/f) relates the distance p of an object from a lens, the distance q of the image of the object from the lens, and the focal length f of the lens. What is this distance of an object from a lens if the image of the object is 7 centimeters from the lens and the focal length of the lens is 3 centimeters?

If you could do that, then I applaud you.
I've been trying to figure it out but I'm so confused.
Please show me how you did it step by step
Thank you to anyone who tries!
You have

$\frac{1}{p}+\frac{1}{7}=\frac{1}{3}$

subtracting the constant gives

$\frac{1}{p}=\frac{4}{21}\Rightarrow{p=\frac{21}{4} }$