Uniform flow with velocity $U$ makes an angle $\theta$ with $y$-axis, as shown in the figure
The velocity potential $(\phi)$, is
1. $\pm U(x\sin\theta+y\cos\theta)$
2. $\pm U(y\sin\theta-x\cos\theta)$
3. $\pm U(x\sin\theta-y\cos\theta)$
4. $\pm U(y\sin\theta+x\cos\theta)$