Electric field of a disk & u-substitution

[Taulant Sholla]

Homework Statement

Calculate the electric field at point P (refer to visual):

Homework Equations

I follow everything - except how the limits of integration for the u-integral (

) are arrived at?

The Attempt at a Solution

u=x² is the smallest value u can have, and u=x²+R² is the greatest value u can have?

 

[TSny]

The lower limit of the u integration should correspond to the lower limit of the r integration (r = 0). So, the lower limit of the u integration is the value of u when r = 0. Similarly for the upper limit.

 

[Taulant Sholla]

Very helpful - thank you!