Well, you should know the concepts of relative coordinate system and world coordinate system. Your triangles should save your relative point list and the center point. Then update the relative point list when rotate for some radius and redraw it. Give some simple code:

#define PI 3.1415926535

typedef struct 
{
    double x, y;
} POINT, *LPPOINT;
typedef class Triangle
{
private:
    POINT pointList[3];
    POINT centerPoint;
public:
    Triangle() { };  // Constructor
    ~Triangle() { };  // Destructor
    BOOL Draw();    // Realize your Draw method
    BOOL Rotate(double theta);    // Rotate method
} TRIANGLE, *LPTRIANGLE;

BOOL TRIANGLE::Rotate(double theta)
{
    double cosVal, sinVal;
    for (int i = 0; i < 3; i++)
    {
        cosVal = cos(theta * PI / 180);
        sinVal = sin(theta * PI / 180);
        // Compute the relative coordinate after rotate
        this->pointList[i].x = this->pointList[i].x * cosVal - this->pointList[i].y * sinVal;
        this->pointList[i].y = this->pointList[i].x * sinVal + this->pointList[i].y * cosVal;
    }
    return this->Draw();

BOOL TRIANGLE::Draw()
{
    // In your draw method, you should change your relative coordinate to world coordinate.
}