​Calculate $\frac { \partial ^ { 2 } f } { \partial x ^ { 2 } }$

Essay

​Calculate $\frac { \partial ^ { 2 } f } { \partial x ^ { 2 } }$ , $\frac { \partial ^ { 2 } f } { \partial y x }$ when defined.
​ $f ( x , y ) = 4 x ^ { 0.8 } y ^ { 0.3 }$ ​
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