For question number 3, cos (5π/6 + B), I am clearly supposed to use the sum and difference identity for cosx(A+B) which is cosAcosB -sinAsinB. At the beginning of section I, sin A and cos B are given on intervals to use while solving questions 1 through 4. Should I plug into the identity the values given at the beginning of the section or instead figure out cosB and sinA based on cosx(A+B) itself, by plugging in A and B.