dy 2 dy y+ ---- x = sec (xy) (y+ ---- x) dx dx dy 2 2 ---(x-xsec (xy)) = ysec (xy)-y dx 2 dy y(sec (xy)-1 ) y --- = ---------------- = - ----- dx 2 x -x(sec (xy)-1) dy 2 ---- x - y d y dx 2y ---- = - ----------- = ---------- 2 x^2 x^2 dx dy 3 2 ----(x^2) - 2y(2x) d y dx ----- = --------------------- 3 dx x^4 -2xy -4xy -6y = ------------- = ---------- x^4 x^3 应该是这样吧 有错请指教^^ ※ 引述《cloistrevoc (convert)》之铭言： : xy=tan(xy) : 1求dy/dx : 2求d^2y/dx^2 : 3求d^3y/dx^3 --

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