Без использования power():
program Primer;
var
a, b, c, s, k, y: real;
begin
writeln('Введите a,b,c: ');
readln(a, b, c);
s := sqrt(3 * (sqr(a) * sqr(a))) / (3 * c) + 3 * b;
k := s + sqrt(abs(sqr(a) * a - b - 2 * c));
y := k - s / (b * c) + sqrt(s);
writeln('y=', y);
end.