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Find the exact value of cosine (alpha beta) given sin alpha = two-fifths for alpha in quadrant ii and cosine beta = one-third for beta in quadrant iv. startfraction 8 startroot 2 endroot startroot 15 endroot over 15 endfraction startfraction 4 startroot 2 endroot startroot 21 endroot over 15 endfraction startfraction 4 startroot 2 endroot minus startroot 21 endroot over 15 endfraction