The Focal Length F of a Lens Is Given by the Formula

Essay

The focal length f of a lens is given by the formula $$\frac { 1 } { f } = \frac { 4 } { d 1 } + \frac { 3 } { d 2 }$$ where d1 is the distance from the object to the lens and d2 is the distance from the lens to the image. Solve the formula for f .