Weird compilor error, need help for assignment

I'm doing an assignment right now regarding headers and overloaded operators and classes and everything, this is my triangle.cpp file defining all my equations or whatever, I get this error and idk what i did wrong
(i can post the whole thing if needed)


cd ~/
g++ Triangle.cpp
Undefined first referenced
symbol in file
main /usr/local/lib/gcc-lib/sparc-sun-solaris2.7/2.95.2/crt1.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

Compilation exited abnormally with code 1 at Thu May 4 17:15:22

//

// Triangle.cpp

//

// Implementation for the Triangle ADT

//



#include <iostream>

#include <cmath>

using namespace std;


#include "Triangle.h"



//////////////////////////////////////////////////////

// Triangle() //
// Triangle.cpp
//
// Implementation for the Triangle ADT
//
// default constructor
Triangle::Triangle() : s1(3), s2(4), s3(5)
{

}


//////////////////////////////////////////////////////

// Triangle(int a, int b, int c)

//////////////////////////////////////////////////////
// Triangle() )
// explicit contructor


Triangle::Triangle(int a, int b, int c) : s1(a), s2(b), s3(c)

{

if (!isValid())
{

cout << "INVALID TRIANGLE! Resetting to <3,4,5>\n";

s1 = 3;

s2 = 4;

s3 = 5;

}

}



//////////////////////////////////////////////////////
// Triangle:erimeter()

//

// The perimeter is the sum of the sides of the triangle. This value

// is returned.

//

int Triangle:erimeter()

{

return (s1 + s2 + s3);

}
//Find the area of the triangle

double Triangle::area ()
{
double s= (s1+s2+s3)/2;
return sqrt(s*(s-s1)*(s-s2)*(s-s3));
}

istream& operator>>(istream& in, Triangle& t)
{

cin >> t.s1 >> t.s2 >> t.s3;

return in;

}

ostream& operator<<(ostream& out, Triangle& t)
{
out<<"<"<<t.s1<<","<<t.s2<<","<<t.s3<<">";

return out;
}


bool Triangle::isValid()
{
if (
s1 < 0 ||
s2 < 0 ||
s3 < 0 ||
s1 + s2 <= s3 ||
s1 + s3 <= s2 ||
s2 + s3 <= s1)
return false;
else
return true;
}

bool Triangle::isRight()
{
if (
(s1*s1)+(s2*s2)==(s3*s3) ||
(s1*s1)+(s3*s3)==(s2*s2) ||
(s3*s3)+(s2*s2)==(s1*s1)
)
return true;
else
return false;
}

bool operator>(Triangle& t1, Triangle& t2)
{
if(
t1.area()>t2.area())
return true;
else
return false;
}

bool operator==(Triangle& t1, Triangle& t2)
{
if(
t1.area()==t2.area())
return true;
else
return false;
}









I NEED HELP!!!! I NEED A GOOD GRADE ON THIS ASSIGNMENT!!! just help me out with my error, thanks a ton

no suggestions from anyone?!?!?!

perhaps it would help if you post Triangle.h
also, put your code between tags to preserve formatting