Выдает ошибку sqrt: DOMAIN error

//---------------------------------------------------------------------------
 
#include <vcl.h>
#include<math.h>
#include<iostream>
#include <stdio.h>
#pragma hdrstop
 
#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma link "CSPIN"
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
}
//---------------------------------------------------------------------------
 
//---------------------------------------------------------------------------
void __fastcall TForm1::FormCreate(TObject *Sender)
{
 
StringGrid1->Cells[0][0] = "N";
StringGrid1->Cells[1][0] = "Xi";
StringGrid1->Cells[2][0] = "Yi";
 
 
 
StringGrid2->Cells[0][0] = "Ñóììà Xi";
StringGrid2->Cells[1][0] = "Ñóììà Yi";
StringGrid2->Cells[2][0] = "Ñóììà Xi^2";
StringGrid2->Cells[3][0] = "Ñóììà Yi^2";
StringGrid2->Cells[4][0] = "Ñóììà Yi*Xi";
StringGrid2->Cells[5][0] = "Êîðåëÿöèÿ r";
 
}
//---------------------------------------------------------------------------//---------------------------------------------------------------------------}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::Button3Click(TObject *Sender)
{
int I,J;
float b,x,c,v,z,d;
double r;
DecimalSeparator = '.';//ãëîáàëüíàÿ âíóòðåííÿÿ ïåðåìåííàÿ
J=StringGrid1->RowCount-2;
for(I=1; I<=J ; I++)
{
b=b+StrToFloat(StringGrid1->Cells[1][I]);
x=x+StrToFloat(StringGrid1->Cells[2][I]);
c=c+(pow(StrToFloat(StringGrid1->Cells[1][I]),2));
v=v+(pow(StrToFloat(StringGrid1->Cells[2][I]),2));
z=z+(StrToFloat(StringGrid1->Cells[1][I]))*(StrToFloat(StringGrid1->Cells[2][I]));
d=StrToFloat(StringGrid1->Cells[0][I]);
r=d*z-b*x/sqrt((d*c-b*b)-(d*v-x*x));
}
StringGrid2->Cells[0][StringGrid2->RowCount-1] = FloatToStr(b);
StringGrid2->Cells[1][StringGrid2->RowCount-1] = FloatToStr(x);
StringGrid2->Cells[2][StringGrid2->RowCount-1] = FloatToStr(c);
StringGrid2->Cells[3][StringGrid2->RowCount-1] = FloatToStr(v);
StringGrid2->Cells[4][StringGrid2->RowCount-1] = FloatToStr(z);
StringGrid2->Cells[5][StringGrid2->RowCount-1] = FloatToStr(r);
}
//---------------------------------------------------------------------------
 
 
 
void __fastcall TForm1::CSpinEdit1Change(TObject *Sender)
{
     StringGrid1->RowCount=CSpinEdit1->Value+2;
     float m;
     m=CSpinEdit1->Value;
     for (int i=1; i<=m; i++)
       StringGrid1->Cells[0][i]=IntToStr(i);
     StringGrid1->Cells[0][m+1]="";
}
//---------------------------------------------------------------------------
 
 
 
void __fastcall TForm1::N5Click(TObject *Sender)
{
Form1->Close();
}
//---------------------------------------------------------------------------
 
 
 
 
void __fastcall TForm1::Button4Click(TObject *Sender)
{
    for(int i = 0; i < StringGrid1->ColCount; i++)
    for(int j = 0; j < StringGrid1->RowCount; j++)
    StringGrid1->Cells[i+1][j+1] = "";
}
//---------------------------------------------------------------------------

r=d*z-b*x/sqrt((d*c-b*b)-(d*v-x*x));