6. (15 points) Suppose given angles a and B such that: \text { (a) (5 points) Find } \cos (\alpha) \text { . } \text { (b) (5 points) Find

} \sin (\beta) \text { . } (c) (5 points) Use the appropriate sum or difference formula to find cos(a – B). \text { - } \alpha \text { is on the second quadrant and } \sin (\alpha)=\frac{\sqrt{3}}{3} \text { ; } \text { - } \beta \text { is on the third quadrant and } \cos (\beta)=-\frac{5}{6} \text { . }