Sin4α+cos4α=(sin²α+cos²α)²-2sin²αcos²α=1-2sin²αcos²α①
(sin²α-cos²α)2=sin²α+cos²α-2sinαcosα=1-2sinαcosα=1/2
sin2α=1/2 sin²2α=1/4
①=1- sin²2α=1-1/4=3/4
Sin4α+cos4α=(sin²α+cos²α)²-2sin²αcos²α=1-2sin²αcos²α①
(sin²α-cos²α)2=sin²α+cos²α-2sinαcosα=1-2sinαcosα=1/2
sin2α=1/2 sin²2α=1/4
①=1- sin²2α=1-1/4=3/4