Quadratic formIn mathematics, a quadratic form is a polynomial with terms all of degree two ("form" is another name for a homogeneous polynomial). For example, is a quadratic form in the variables x and y. The coefficients usually belong to a fixed field K, such as the real or complex numbers, and one speaks of a quadratic form over K. If , and the quadratic form equals zero only when all variables are simultaneously zero, then it is a definite quadratic form; otherwise it is an isotropic quadratic form.
Definite quadratic formIn mathematics, a definite quadratic form is a quadratic form over some real vector space V that has the same sign (always positive or always negative) for every non-zero vector of V. According to that sign, the quadratic form is called positive-definite or negative-definite. A semidefinite (or semi-definite) quadratic form is defined in much the same way, except that "always positive" and "always negative" are replaced by "never negative" and "never positive", respectively.
Kim Il SungKim Il Sung (ˈkɪm_ˈɪlˈsʌŋ,_-ˈsʊŋ; , kimils͈ʌŋ; 15 April 1912 – 8 July 1994) was a Korean politician and the founder of North Korea. He ruled the country from the country's establishment in 1948 until his death in 1994. Afterwards, he was declared its eternal president. His birth name was Kim Song Ju (). He held the posts of the Premier from 1948 to 1972 and President from 1972 to 1994. He was the leader of the Workers' Party of Korea (WPK) from 1949 to 1994 (titled as Chairman from 1949 to 1966 and as General Secretary after 1966).
Kim Jong IlKim Jong Il (,kɪm_ʤɒŋˈɪl; ; kim.dzɔŋ.il; also transcribed as Kim Jong-il and born Yuri Irsenovich Kim; 16 February 1941 or 1942 – 17 December 2011) was a North Korean politician who was the second supreme leader of North Korea from 1994 to 2011. He led North Korea from the 1994 death of his father Kim Il Sung, the first Supreme Leader, until his own death in 2011, when he was succeeded by his son, Kim Jong Un. In the early 1980s, Kim had become the heir apparent for the leadership of the Democratic People's Republic of Korea (DPRK) and assumed important posts in the party and army organs.
AngleIn Euclidean geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle. Angles formed by two rays are also known as plane angles as they lie in the plane that contains the rays. Angles are also formed by the intersection of two planes; these are called dihedral angles. Two intersecting curves may also define an angle, which is the angle of the rays lying tangent to the respective curves at their point of intersection.
Venn diagramA Venn diagram is a widely used diagram style that shows the logical relation between sets, popularized by John Venn (1834–1923) in the 1880s. The diagrams are used to teach elementary set theory, and to illustrate simple set relationships in probability, logic, statistics, linguistics and computer science. A Venn diagram uses simple closed curves drawn on a plane to represent sets. Very often, these curves are circles or ellipses.
Euler diagramAn Euler diagram (ˈɔɪlər, ) is a diagrammatic means of representing sets and their relationships. They are particularly useful for explaining complex hierarchies and overlapping definitions. They are similar to another set diagramming technique, Venn diagrams. Unlike Venn diagrams, which show all possible relations between different sets, the Euler diagram shows only relevant relationships. The first use of "Eulerian circles" is commonly attributed to Swiss mathematician Leonhard Euler (1707–1783).
Right angleIn geometry and trigonometry, a right angle is an angle of exactly 90 degrees or /2 radians corresponding to a quarter turn. If a ray is placed so that its endpoint is on a line and the adjacent angles are equal, then they are right angles. The term is a calque of Latin angulus rectus; here rectus means "upright", referring to the vertical perpendicular to a horizontal base line. Closely related and important geometrical concepts are perpendicular lines, meaning lines that form right angles at their point of intersection, and orthogonality, which is the property of forming right angles, usually applied to vectors.
Angle trisectionAngle trisection is a classical problem of straightedge and compass construction of ancient Greek mathematics. It concerns construction of an angle equal to one third of a given arbitrary angle, using only two tools: an unmarked straightedge and a compass. In 1837, Pierre Wantzel proved that the problem, as stated, is impossible to solve for arbitrary angles. However, some special angles can be trisected: for example, it is trivial to trisect a right angle (that is, to construct an angle of 30 degrees).
5GIn telecommunications, 5G is the fifth-generation technology standard for broadband cellular networks, which cellular phone companies began deploying worldwide in 2019, and is the planned successor to the 4G networks which provide connectivity to most current cellphones. Like its predecessors, 5G networks are cellular networks, in which the service area is divided into small geographical areas called cells. All 5G wireless devices in a cell are connected to the Internet and telephone network by radio waves through a local antenna in the cell.
2G2G is a short notation for second-generation cellular network, a group of technology standards employed for cellular networks. 2G was commercially launched on the GSM standard in Finland by Radiolinja (now part of Elisa Oyj) in 1991. After 2G was launched, the previous mobile wireless network systems were retroactively dubbed 1G. While radio signals on 1G networks are analog, radio signals on 2G networks are digital, though both systems use digital signaling to connect cellular radio towers to the rest of the mobile network system.
