分子=1-cos^4α-sin^4α=1-[cos^4α+sin^4α]
=1-[(cos²α+sin²α)²-2cos²αsin²α]=2cos²αsin²α
分母=1-cos^6α-sin^6α=1-(cos^6α+sin^6α)
=1-(cos²α+sin²α)(cos^4α+sin^4α-cos²αsin²α)
=1-(cos^4α+sin^4α-cos²αsin²α)
=1-[(cos²α+sin²α)²-3cos²αsin²α]=3cos²αsin²α
分子/分母=2cos²αsin²α/3cos²αsin²α=2/3