theorem :: DIFF_4:5

for k, x0, x1, x2, x3 being Real
for f being Function of REAL,REAL st ( for x being Real holds f . x = k / (x ^2) ) & x0 <> 0 & x1 <> 0 & x2 <> 0 & x3 <> 0 & x0,x1,x2,x3 are_mutually_distinct holds
[!f,x0,x1,x2,x3!] = (k * (((1 / ((x1 * x2) * x0)) * (((1 / x0) + (1 / x2)) + (1 / x1))) - ((1 / ((x2 * x1) * x3)) * (((1 / x3) + (1 / x1)) + (1 / x2))))) / (x0 - x3)