sin2a=1-根号2*(a-π/4)
2sina*cosa=sin²a+cos²a-根号2*(a-π/4)
(sina-cosa)²=根号2*(a-π/4)
1/2sin²(a-π/4)=根号2*(a-π/4)
sin²(a-π/4)=2根号2*(a-π/4)
a∈【0,2π】,
(a-π/4)∈【-π/4,7π/4】,
0<2根号2*(a-π/4)<1
π/4<a<(根号2/4 +π/4 )
sin2a=1-根号2*(a-π/4)
2sina*cosa=sin²a+cos²a-根号2*(a-π/4)
(sina-cosa)²=根号2*(a-π/4)
1/2sin²(a-π/4)=根号2*(a-π/4)
sin²(a-π/4)=2根号2*(a-π/4)
a∈【0,2π】,
(a-π/4)∈【-π/4,7π/4】,
0<2根号2*(a-π/4)<1
π/4<a<(根号2/4 +π/4 )