public void TriangleTest()
        {
            Triangle t = new Triangle(5, 7, 9);

            Assert.AreEqual(t.Perimetr(), 21);

            RightTriangle rt = new RightTriangle(3, 4, 5);

            Assert.AreEqual(rt.Perimetr(), 12);
            Assert.AreEqual(rt.Area(), 6);
        }