R+2r+(r^2/R)
微分したらどうなる?
つーか、どうすれば、1-(r^2/R^2)になるんだ?
고민일
R+2 r+(r^2/R)
미분 하면 어떻게 된다?
개-인가, 어떻게 하면,1-(r^2/R^2)가 된다?
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