I need help with 6, 7, and 8.

[tex]cos\ u=-\dfrac{15}{15}\implies sin\ u=\dfrac{\sqrt{210}}{15}\\\\sin\ v=-\dfrac{5}{13}\implies cos\ v=-\dfrac{12}{13}[/tex]6.Answer: [tex]\bold{\dfrac{12\sqrt{15}+5\sqrt{210}}{195}}[/tex]Step-by-step explanation:[tex]cos(u+v)=cosu\cdot cosv-sinu\cdot sinv\\\\.\qquad\qquad=\dfrac{-\sqrt{15}}{15}\cdot \dfrac{-12}{13}-\dfrac{\sqrt{210}}{15}\cdot \dfrac{-5}{13}\\\\\\.\qquad\qquad=\dfrac{12\sqrt{15}}{195}+\dfrac{5\sqrt{210}}{195}\\\\\\.\qquad\qquad=\boxed{\dfrac{12\sqrt{15}+5\sqrt{210}}{195}}[/tex]7.[tex]\bold{\dfrac{-12\sqrt{210}-5\sqrt{15}}{195}}[/tex]Step-by-step explanation:[tex]sin(u-v)=sinu\cdot cosv-cosu\cdot sinv\\\\.\qquad\qquad=\dfrac{\sqrt{210}}{15}\cdot \dfrac{-12}{13}-\dfrac{-\sqrt{15}}{15}\cdot \dfrac{-5}{13}\\\\\\.\qquad\qquad=\dfrac{-12\sqrt{210}}{195}-\dfrac{5\sqrt{15}}{195}\\\\\\.\qquad\qquad=\boxed{\dfrac{-12\sqrt{210}-5\sqrt{15}}{195}}[/tex]8.Answer: [tex]\bold{-\dfrac{19}{67}}[/tex]Step-by-step explanation:[tex]tan\ u=-\dfrac{3}{4}\\\\cos\ v=-\dfrac{12}{13}\implies tan\ v=\dfrac{5}{13}\\\\\\\\tan(u+v)=\dfrac{tan\ u+tan\ v}{1-tan\ u\cdot tan\ v}\\\\\\.\qquad\qquad=\dfrac{\frac{-3}{4}+\frac{5}{13}}{1-(\frac{-3}{4}\cdot \frac{5}{13})}\\\\\\.\qquad\qquad=\dfrac{\frac{-39}{52}+\frac{20}{52}}{\frac{52}{52}+\frac{15}{52}}\\\\\\.\qquad\qquad=\boxed{-\dfrac{19}{67}}[/tex]