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W1 = L1*A1*ρ ρ:銅比重
W2 = L1*A2*ρ
∴ Ll*A1=L2*A2
L1/L2 = A2/A1 1-(L1/L2) = 1-(A2/A1) = R% L1/L2 = 1-R%
∴ E% = (L2-L1)/L1 = (L2/L1)-1=1/(L1/L2)-1=1/(1-R%)-1
= R%/(1-R%)
R%=E%/(1+E%)
若E%=26%
R = 0.26/(1+0.26) =0.206 即20.6%
就是這樣來的。
