Sorry to be a pain, but could you shed light onto how you got that answer?
Use the double angle formula: cos(2x) = 2cos˛(x) - 1
A single flow'r he sent me, since we met./All tenderly his messenger he chose;
Deep-hearted, pure, with scented dew still wet - One perfect rose.
I knew the language of the floweret;/'My fragile leaves,' it said, 'his heart enclose.'
Love long has taken for his amulet/One perfect rose.
Why is it no one ever sent me yet/One perfect limousine, do you suppose?
Ah no, it's always just my luck to get/One perfect rose.