int triangleAmount = 6;
GLfloat twicePi = 2.0f * 3.14;

glBegin(GL_TRIANGLE_FAN);
glVertex2f(x_1,y_1);

for(int i = 0; i <= triangleAmount; i++)
{
glVertex2f(
    x_1+(6.0*cos(i*twicePi/triangleAmount))*4,
    y_1+(6.0*sin(i*twicePi/triangleAmount))*4);
}
glEnd();
glFlush();