думаю легкие задания=)

#include <iostream>
#include <math.h>
using namespace std;
 
class Vector {
    float x1, x2, x3;
 
public:
    Vector (float _x1 = 0.0, float _x2 = 0.0, float _x3 = 0.0)
    {
    x1 = _x1;
    x2 = _x2;
    x3 = _x3;
    };
 
    void Print(){
        cout << "x1 = " << x1 << ", x2 = " << x2 << ", x3 = " << x3 << ";\n"; 
    };  
 
    float Length(){
        return sqrt( x1*x1 + x2*x2 + x3*x3 );
    };  
 
    Vector operator+( Vector &ob );
    Vector operator-( Vector &ob );
 
    float friend Scalar ( Vector &ob1, Vector &ob2 );
    float friend Cosin ( Vector &ob1, Vector &ob2 );
    
};
 
float Scalar( Vector &ob1, Vector &ob2 )
{
    return ob1.x1*ob2.x1 + ob1.x2*ob2.x2 + ob1.x3*ob2.x3;
}
 
float Cosin ( Vector &ob1, Vector &ob2 )
{
    if ( Scalar( ob1, ob2 ) == 0 )
        return 1.0;
    else
        return Scalar( ob1, ob2 )/ob1.Length()/ ob2.Length() ;
}
 
Vector Vector::operator+( Vector &ob )
{
    return Vector( x1 + ob.x1, x2 + ob.x2, x3 + ob.x3 );
}
 
Vector Vector::operator-( Vector &ob )
{
    return Vector( x1 - ob.x1, x2 - ob.x2, x3 - ob.x3 );
}
 
 
int main ()
{
 
    Vector a1(1,1,1), a2(1), a3;
 
    a3 = a2 + a1;
    a3.Print();
    a3 = a3 - a1;
    a3.Print();
    Vector b1(1), b2(1,2);
    cout <<" cos = " << Cosin ( b1, b2 ) << endl;
 
    system("PAUSE");
    exit (0);
}