differentiating circuit voltage gain
It doesn't matter here that 1/j=-j -meaning -ve phase shift , but it does matter that 1/|Zin|=1/√(1+1) = 1/√2= 1/ 1.414= 0.707   

meaning \$A_V= - \dfrac{R_f}{\sqrt{(R_{in}+2πfC)}}= -5/√2 \$

Don't forget your Vector Algebra


 But if you do, You may find the above handy in future







simulate this circuit &ndash; Schematic created using CircuitLab