Find $\displaystyle {\cos{{\left(\alpha+\beta\right)}}}$ exactly, given $\displaystyle {\cos{\alpha}}=-\frac{{3}}{{4}}$  and $\displaystyle {\sin{\beta}}=-\frac{{2}}{{5}}$ where $\displaystyle \alpha$ terminates in quadrant II and $\displaystyle \beta$ terminates in quadrant IV. Be sure to reduce your final result completely.