Find the Differential of the Function $f ( x , y ) = \sqrt { x ^ { 2 } + y ^ { 2 } }$

Essay

Find the differential of the function $f ( x , y ) = \sqrt { x ^ { 2 } + y ^ { 2 } }$ at the point (3, 4).
A point is measured to be 3 units from the y-axis with an error of ±0.01 and 4 units from the x-axis with an error of ±0.02.Approximate the error in computing its distance from the origin.