For
p,q∈R, consider the real valued function\n
f(x)=(x−p)2−q,x∈R and
q>0. Let\n
a1,a2,a3 and
a4 be in an arithmetic progression\n with mean
p and positive common difference. If\n
∣f(ai)∣=500 for all
i=1,2,3,\n 4 , then the absolute difference between the roots of
f(x)=0 is