Mathematics is the study and practice of rigorous inference about abstract structures. It includes many practical results concerning quantity and measure, such as calculations involving numbers, financial accounting, geometric construction of building, astronomical calculations, calendar dating, telling time, engineering, physics, chemistry, etc. but also more abstract issues such as establishing the conditions under which certain kinds of equations and formulas have solutions. [[Applied mathematics]] concerns the use of mathematical methods for practical purposes. [[Pure mathematics]] involves reasoning about abstract structures. The main areas are:
* [[Algebra]]. Broadly, speaking algebra concerns 'addition' and 'multiplication', but in the widest possible sense. The objects that are being added or multiplied can be numbers, as in [[Number theory]], but they can also can be more general structures such as [[matrix|matrices]], [[functions]], [[polynomials]], [[vectors]] or many others. Concentrating on addition and multiplication does not exclude subtraction or division, since subtraction is formally considered to be addition of an [[additive inverse]] and division is considered to be multiplication by a [[multiplicative inverse]]. That is, subtracting 3 from 2 is rigorously defined to adding the number -2 to 3. Minus two is called the additive inverse of +2. Similarly, dividing 3 by 2 is formally defined in terms of multiplying 3 by (1/2), where 1/2 is the multiplicative inverse of 2. Abstract algebra is the study of [[algebraic structures]] such as [[Group (mathematics)|groups]], [[Ring (mathematics)|rings]], and [[Field (mathematics)|fields]].