4319.sagews

var('x')
f(x)=x*(750-5*x)/2
plot(f,(x,0,150))

diff(f)

x |--> -5*x + 375

diff(diff(f))

x |--> -5

solve(diff(f),x)

[x == 75]

[f(0),f(150),f(75.0)]

[0, 0, 14062.5000000000]

plot(diff(f), (x,0,150))