Let z = f (XY, x ^ 2-y ^ 2), where f has the second order continuous partial derivative, find a ^ Z / ax ^ 2

Analysis:
az/ax=yf[1]+2xf[2]
a^2z/ax^2
=y(yf[11]+2xf[12])+2f[2]+2x(yf[21]+2xf[22])
=y^2f[11]+4xyf[12]+4x^2f[22]+2f[2]
Note: F [] denotes the partial derivative of the subscript variable in square brackets. Here 1 represents xy and 2 represents x ^ 2-y ^ 2

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