The vector $A=5i+6j$ is rotated through an $\mathrm{\angle}45$ about the Z axis in the anticlockwise direction. What is the resultant vector?

My attempt: I tried to calculate the resultant vector by using the equation, $R=\sqrt{{A}^{2}+{B}^{2}+2ABCos\theta}$

since it is rotated in anticlockwise direction its direction changes. Any hint will be appreciated.

My attempt: I tried to calculate the resultant vector by using the equation, $R=\sqrt{{A}^{2}+{B}^{2}+2ABCos\theta}$

since it is rotated in anticlockwise direction its direction changes. Any hint will be appreciated.