If $\displaystyle \alpha$ is a Quadrant $\displaystyle {I}{V}$  angle with $\displaystyle {\cos{{\left(\alpha\right)}}}={\frac{{\sqrt{{{16}}}}}{{{16}}}}$ , and  $\displaystyle {\sin{{\left(\beta\right)}}}={\frac{{\sqrt{{{4}}}}}{{{4}}}}$ , where $\displaystyle {\frac{{\pi}}{{{2}}}}<\beta<\pi$ , find

(a) $\displaystyle {\sin{{\left(\alpha+\beta\right)}}}$ Preview Question 6 Part 1 of 2  

(b) $\displaystyle {\cos{{\left(\alpha-\beta\right)}}}$ Preview Question 6 Part 2 of 2