Blackboard bold is a typeface style that is often used for certain symbols in mathematical texts, in which certain lines of the symbol (usually vertical or near-vertical lines) are doubled. The symbols usually denote number sets.
A letter of the alphabet drawn with doubled vertical strokes is called doublestruck, or sometimes blackboard bold (because doublestruck characters provide a means of indicating bold font weight when writing on a blackboard).
real numbersR = real numbers, Z = integers, N=natural numbers, Q = rational numbers, P = irrational numbers.
The blackboard bold 1, , usually represents the identity or the neutral multiplicative member of a set/group/field. In general: , for all .
The set of real numbers is denoted using the symbol R or. and is sometimes called "the reals". Real numbers can be thought of as points on an infinitely long line called the number line or real line, where the points corresponding to integers are equally spaced.
The symbol ∈ indicates set membership and means “is an element of” so that the statement x∈A means that x is an element of the set A. In other words, x is one of the objects in the collection of (possibly many) objects in the set A.
When putting a + sign at the top, it means only the positive whole numbers, starting from 1, then 2 and so on. N stands for the set of all natural numbers, and in most definitions, it starts from 1,2,3,..,n. Therefore, it can be assumed that Z+ and N are the same sets since they contain the same elements.
Z+ is the set of all positive integers (1, 2, 3, ...), while Z- is the set of all negative integers (..., -3, -2, -1). Zero is not included in either of these sets .
The real numbers include the positive and negative integers and fractions (or rational numbers) and also the irrational numbers.
Someone who's bold is daring and brave. You might show how bold you are by climbing onto the roof of your house, or by speaking up when you see someone being treated unfairly. When you act in a bold way, you're taking some kind of risk; you could be risking physical danger, embarrassment, or your reputation.
Bold, brazen, forward, presumptuous may refer to manners in a derogatory way. Bold suggests impudence, shamelessness, and immodesty: a bold stare. Brazen suggests the same, together with a defiant manner: a brazen liar.
Bold, bold face, or bold font creates the appearance of darker text by applying a thicker stroke weight to the letters. Using bold text in a body paragraph helps emphasize a remark or comment.