How to sketch the graph of $\displaystyle \sin x -3 \cos x$

i know i can do this : $\displaystyle \sin x -3 \cos x = \sqrt{10} \sin({\color{red}x - 71.6})$

How can i sketch this when the one in red is not $\displaystyle \theta $or $\displaystyle 2 \theta$

Thanks .