Cramer's Rule.
A problem posed by Hadamard attempts to find the largest value for one of these entities given the elements of a set. Differential equations can be solved using one called the Wronskian, and these entities can be computed using the technique of expansion by minors. Ratios of these are used to find solutions to systems of equations via (*) Cramer's Rule. If this value is zero, the matrix associated with it is singular. For 10 points, name this mathematical concept that, for a two by two matrix a b; c d, is equal to a d minus b c.
A problem posed by Hadamard attempts to find the largest value for one of these entities given the elements of a set.
determinant