Putting the sign convention properly
\(\frac{1}{{( - v)}} = \frac{{ - 1}}{{( - u)}} + \frac{1}{{( - f)}}\) ==> \(\frac{1}{v} = - \frac{1}{u} + \frac{1}{f}\)
Comparing this equation with \(y = mx + c\)
\(Slope\) \(= m = tan\)\(\theta\) \(= -1 \)==> \(\theta\) \(= 135°\) or \(-45°\) and intercept \(C = + \frac{1}{f}\)