Function help with plugging in answer

function [out] = p4(x)
L = 600;
E = 50000;
I = 30000;
w0 = 2.5;
out = (w0/120*E*I*L) * (-5*x^4 + 6*L^2*x^2 - L^4); % derivative of y(x)
end      % I am getting x = 268.3282

Above is a function p4 I made. I am trying to solve for where p4 = 0, or the slope of y(x) = 0. I have plugged in the equation into symbolab.com and solved for x and it confirmed my result, x = 268.3282, however when I plug that value into p4, it does not equal 0, this is the value I recieve: p4(x) = 858306.884766. I do not understand, could someone please explain.

[Matthew Covington]

out = w0/(120*E*I*L) * (-5*x^4 + 6*L^2*x^2 - L^4); % derivative of y(x)

I figured it out, it was a perthesis error. I had it as (w0/120*E*I*L) instead of w/(120*E*I*L)

[Asad (Mehrzad) Khoddam]

Yes, for the delflection of the beams, EI should be on the bottom of the fraction