1.When the object is at distances u1u_1u1 and u2u_2u2, the images formed by the same lens are real and virtual respectively and of the same size. Then the focal length of the lens is:a.12u1u2\dfrac{1}{2}\sqrt{u_1 u_2}21u1u2b.u1+u22\dfrac{u_1 + u_2}{2}2u1+u2c.u1u2\sqrt{u_1 u_2}u1u2d.u1+u2\sqrt{u_1 + u_2}u1+u2Login to continueOnly logged in users canattempt or see the solution.