сos²π/8=(1+cos(π/4))/2=(1+√2/2)/2=(2+√2)/4
sin(π/8)*cos(3π/8)=sin(π/8)*cos(π/2-π/8)=sin²(π/8)=1-((2+√2)/4)
сos²π/8+sin(π/8)*cos(3π/8)=
(2+√2)/4+1-((2+√2)/4)=(2+√2+4-2-√2)/4=1
сos²π/8=(1+cos(π/4))/2=(1+√2/2)/2=(2+√2)/4
sin(π/8)*cos(3π/8)=sin(π/8)*cos(π/2-π/8)=sin²(π/8)=1-((2+√2)/4)
сos²π/8+sin(π/8)*cos(3π/8)=
(2+√2)/4+1-((2+√2)/4)=(2+√2+4-2-√2)/4=1