theorem Th27: :: DIFF_2:27

for x0, x1, a, b, c being Real
for f being Function of REAL,REAL st ( for x being Real holds f . x = ((a * (x ^2)) + (b * x)) + c ) & x0 <> x1 holds
[!f,x0,x1!] = (a * (x0 + x1)) + b