求z=sin(x+2y)的二阶偏导数
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z=sin(x+2y)
∂z/∂x
=cos(x+2y) .∂/∂x (x+2y)
=cos(x+2y) . (1)
=cos(x+2y)
∂^2z/∂x^2 =-sin(x+2y)
∂z/∂y
=cos(x+2y) .∂/∂y (x+2y)
=cos(x+2y) . (2)
=2cos(x+2y)
∂^2z/∂y^2 = -4sin(x+2y)
∂^2z/∂x∂y
=∂^2z/∂y∂x
=∂/∂y(∂z/∂x)
=-2sin(x+2y)
∂z/∂x
=cos(x+2y) .∂/∂x (x+2y)
=cos(x+2y) . (1)
=cos(x+2y)
∂^2z/∂x^2 =-sin(x+2y)
∂z/∂y
=cos(x+2y) .∂/∂y (x+2y)
=cos(x+2y) . (2)
=2cos(x+2y)
∂^2z/∂y^2 = -4sin(x+2y)
∂^2z/∂x∂y
=∂^2z/∂y∂x
=∂/∂y(∂z/∂x)
=-2sin(x+2y)
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