posted by missfubu-c .
find the functional values requested in the problem F(x)=x^2-25t
if f(x) = x^2 - 25t
f(5t) = (5t)^2 - 25t = 25t^2 - 25t
so the second one in the same way.
Notice we had a function of x, that is, f(x)
so only the terms that contain x's are affected in the substitution, unless you have a typo.