can anybody explain me how to use reals with big range like 10^18 or 10^19 more precisely in pascal?

If you need real numbers with best affordable precision - use long double ("extended" in pascal).

Edited by author 06.01.2013 23:12

I knew the solution was k=1 or trunc((1+12*b*b/(a*a)-3*c/a)). but i could not take precision.

F**k, spoiler =(
Then you don't need real numbers here - long long (int64 in Pascal) is enough to solve it