Slope of deflection of beam at center

[fonseh]

Homework Statement

in the first photo , it's stated that the dy/dx at center = 0 , however , in the second photo (website) , it's stated that the dy/dx at the boundary = 0 ,which is correct ? I'm confused now
http://www.geom.uiuc.edu/education/calc-init/static-beam/support.html

Homework Equations

The Attempt at a Solution

 

[fonseh]

Bump