Here is the requirement for coding, first line of coding is the range of x and y, vecyx is dL/dx, vecy is dL/dy. Those are provided by the requriement.

Then following the requirement's description. I used V=[ ] ; length(v) to calculate the length, but it just come up one result. But according to the description, the reulst should be an array. So how do i code it? Many thanks!!!!!!

`[x,y]=meshgrid(0:0.01:50, 0:0.01:30);vecx=((2*x-30)/(2*sqrt(850-30*x-50*y+x.^2+y.^2))+((2*x-20)/(2*sqrt(125-20*x-10*y+x.^2+y.^2)))+((2*x-80)/(2*sqrt(1700-80*x-20*y+x.^2+y.^2))));vecy=((2*y-50)/(2*sqrt(850-30*x-50*y+x.^2+y.^2))+((2*y-10)/(2*sqrt(125-20*x-10*y+x.^2+y.^2)))+((2*y-20)/(2*sqrt(1700-80*x-20*y+x.^2+y.^2))));V=[vecx vecy];L=length(V);`

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