Hello, I'm receiving an error when I compile my code for "project06.triangle.cpp". How can i fix the problem without changing any code in the header file?

Here's the code for project06.triangle.cpp:
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#include "/user/cse232/Projects/project06.triangle.h"
#include <cmath>
#include <iostream>
#include <ostream>
#include <iomanip>

Triangle::Triangle( double SA, double SB, double SC )
{
SideA = SA;
SideB = SB;
SideC = SC;
}
void Triangle::validate()
{
if (SideA > 0.0 && SideB > 0.0 && SideC > 0.0)
{
Valid = true;
}
else
{
Valid = false;
}
}
bool Triangle::is_valid()
{
validate();
return Triangle.valid;
}

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and the code for project06.triangle.h:
*********************************************
#ifndef TRIANGLE_
#define TRIANGLE_

using namespace std;
#include <iostream>

class Triangle
{
private:
double SideA, SideB, SideC;
bool Valid;
void validate();
public:
Triangle( double = 0.0, double = 0.0, double = 0.0 );
bool is_valid() const;
}
*******************************************
and I'm receiving the following error:

project06.triangle.cpp:177: error: prototype for 'bool Triangle::is_valid()' does not match any in class 'Triangle'
/user/cse232/Projects/project06.triangle.h:44: error: candidate is: bool Triangle::is_valid() const