In linear algebra, the adjugate or classical adjoint of a square matrix is the transpose of its cofactor matrix. It is also occasionally known as adjunct matrix, though this terminology appears to have decreased in usage. The concept of the inverse of a matrix is a multidimensional generalization of the concept of reciprocal of a number: the product between a number and its reciprocal is equal to 1; the product between a square matrix and its inverse is equal to the identity matrix. The inverse of A is A-1 only when A
×
A-1 = A-1×
A = I. To find the inverse of a 2×
2 matrix: swap the positions of a and d, put negatives in front of b and c, and divide everything by the determinant (ad-bc).