cos(x+y) = cosx•cosy-sinx•siny
cos14°20'•cos15°40'-sin14°20'•sin15°40' = cos(14°20'+15°40') = cos(29°60') = cos30° = ✓3/2
cos(x+y) = cosx•cosy-sinx•siny
cos14°20'•cos15°40'-sin14°20'•sin15°40' = cos(14°20'+15°40') = cos(29°60') = cos30° = ✓3/2