Lời giải :
program hotrotinhoc ;
var a,b,h : integer ;;
s: real;
begin
write('Nhap day a='); readln(a);
write('Nhap day b='); readln(b);
write('Nhap chieu cao h='); readln(h);
s:=((a+b)/2)*h ;
write('Dien tich hinh thang la :',s);
readln
end.