A circuit shown consists of three resistors, one capacitor, 2 ideal AC voltmeters and alternating voltage source of angular frequency $\omega$. Take  $R\omega C=1$. If the reading of  $V_1$ is V, then the reading of  $V_2$ is 

Let voltage phasors along be  $PA,AE$  be x, 2x

And voltage phasors along QB, BF be y, y. (as  $R=\frac{1}{\omega C}$).
The phasors diagram representing them can be drawn as shown

So phasor length AB (i.e; reading of  $V_2$$$) is= $\sqrt{x^2+y^2-2xy\cos {45}^{°}}$(using cosine rule in $\Delta PAB$)
Also  $x+2x=V$ and  $\sqrt{2y}=V$
$\Rightarrow$ Reading of  $V_2=\frac{V}{3}\sqrt{\frac{5}{2}}$