\(m_1 m_2=1\) which is a fact.
Here the lens is moved between the object and the screen.
\(v\) and \(u\) interchange values between the two positions a clear image is formed on the screen.
If \(m_1=\frac{v}{u}\) and \(m_2=\frac{u}{v}\)
\(m_1 m_2=1\)