a=2√2，C=2A=45°，A=22.5°，B=180°-22.5°-45°=112.5°
正弦定理
a/sinA=b/sinB=c/sinC
sinA=sin22.5°，根据cos2α=cos²α-sin²α=1-2sin²α,sinα=√[(1-cos2α)/2]
sin22.5°=√[(1-cos45°)/2]=√[(1-√2/2)/2]=√[(2-√2)/4]=√(2-√2)/2
sinB=sin112.5°=sin(90°+22.5°)=cos22.5°
根据cos2α=cos²α-sin²α=2cos²α-1,cosα=√[(1+cos2α)/2]
cos22.5°=√[(1+cos45°)/2]=√[(1+√2/2)/2]=√[(2+√2)/4]=√(2+√2)/2
b=(a/sinA)sinB=(2√2÷√(2-√2)/2)√(2+√2)/2=2√2×(2+√2)/(2-√2)
=2√2×(6+4√2)/2
=6√2+8
c=(a/sinA)sinC=(2√2÷√(2-√2)/2)×√2/2
=2√2×2/√(2-√2)×√2/2
=4/√(2-√2)
=2（2+√2）=4+2√2
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