分子=1-cos ^4α－sin ^4α=1-[cos ^4α+sin ^4α]
=1-[(cos² α+sin²α)²-2cos²αsin²α]=2cos²αsin²α
分母=1-cos ^6α－sin ^6α=1-(cos ^6α+sin ^6α)
=1-(cos² α+sin²α)(cos^4 α+sin^4α-cos² αsin²α)
=1-(cos^4 α+sin^4α-cos² αsin²α)
=1-[(cos² α+sin²α)²-3cos² αsin²α]=3cos² αsin²α
分子/分母=2cos²αsin²α/3cos² αsin²α=2/3