You've got a couple of missing begin...end blocks here. Because of that, you're evaluating:
raiz2 := (-b -
sqrt(d))/(2*a);
even when d is negative, which would cause your program to abort (because of the part in
bold text). You also have some unnecessary begin..end blocks.
Restructuring your code around a bit, I ended up with:
program FormulaResolvente;
uses
crt;
var
A : real;
B : real;
C : real;
D : real; {o k ta dentro da raiz kuadrada da formula resolvente}
X : real; {coordenada X do vertice}
raiz1 : real;
raiz2 : real;
Begin
clrscr;
writeln( 'Introduz o valor de A:' );
readln( A );
writeln( 'Introduz o valor de B:' );
readln( B );
writeln( 'Introduz o valor de C:' );
readln( C );
d:= (b*b)-(4*a*c);
if d < 0 then
writeln('Raizes de nºs negativos nao existem Razz')
else
begin
raiz1:= (-b+sqrt(d))/(2*a);
raiz2:= (-b-sqrt(d))/(2*a);
writeln('1ª Raiz = ',raiz1);
writeln('2ª R aiz = ',raiz2);
X:= (raiz1+raiz2)/2;
writeln('Coordenada X do vertice : ',X);
writeln('Coord enada Y do vertice : ',(A*sqr(x))+(B*X)+C);
end;
while not keypressed do;
end.