cos(π/4)=√2/2=2cos²(π/8)-1=1-2sin²(π/8)因为sin(π/8)>0,cos(π/8)>0所以sin(π/8)=√[(1-√2/2)/2]=√[(2-√2)/4]=√(2-√2)/2cos(π/8)=√[(1+√2/2)/2]=√[(2+√2)/4]=√(2+√2)/2...