почему в моей программе выскакивает error 200 Division by zero

program twice;
var x,y,z:integer;
x1,x2,t,e,x3:real;
a,b,c,x4:word;
begin
write(' Tne twice number of the enter x,y,z ? ', x,y,z);
x1:=x/(y*z);
if (x>0) and (x<10) and (y<=1) then
begin
write(' Tne enter integer for you x,y,z= ', x,y,z );
x2:=x*x*x+4*y*y-3*z+5;
writeln(' You answer for x2 = ', x2:3:6 );
end
else
if (x<0) and (x>10) and (y>=1) then
begin
write(' Tne enter integer for you s,t,e= ', t,e );
x3:=(2*t*t-(cos(e)/sin(e)))/t*t*t*(sin(e)/cos(e))*3;
writeln(' You answer for x3 = ', x3:8:3 );
end
else
begin
if (x>0) and (y=3) then
write(' Tne enter integer for you a,b,c= ', a,b,c );
x4:=2*a*a+3*b-c;
writeln(' You answer for x4 = ', x:10);
readln;
end
end.