Multiplicative Inverse
In a monoid or multiplicative group where the operation is a product ·, the multiplicative inverse of any element g is the element g^(-1) such that g·g^(-1)=g^(-1)·g=1, with 1 the identity element.
The multiplicative inverse of a nonzero number z is its reciprocal 1/z (zero is not invertible). For complex z=x+iy!=0,
The inverse of a nonzero real quaternion h=x+yi+vj+wk (where x,y,v,w are real numbers, and not all of them are zero) is its reciprocal
where alpha=x^2+y^2+v^2+w^2.
The multiplicative inverse of a nonsingular matrix is its matrix inverse.
To detect the multiplicative inverse of a given element in the multiplication table of finite multiplicative group, traverse the element's row until the identity element 1 is encountered, and then go up to the top row. In this way, it can be immediately determined that -i is the multiplicative inverse of i in the multiplicative group C_4 formed by all complex fourth roots of unity.
See also
Additive Inverse, Invertible Element, Multiplicative Identity, Multiplicative GroupThis entry contributed by Margherita Barile
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Barile, Margherita. "Multiplicative Inverse." From MathWorld--A Wolfram Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/MultiplicativeInverse.html