Rt is the abbreviation for right-angled triangle, which means a triangle with one angle being a right angle. There are two types of right-angled triangles, namely the ordinary right-angled triangle and the isosceles right-angled triangle. They satisfy the Pythagorean theorem and have certain special properties and determination methods. The side opposite to the right angle in a right-angled triangle is also called the “hypotenuse”, while the shorter of the two legs is called the “adjacent side” and the longer leg is called the “opposite side”.