# Function invmod Calculate the (modular) multiplicative inverse of a modulo b. Solution to the equation `ax ≣ 1 (mod b)` See https://en.wikipedia.org/wiki/Modular_multiplicative_inverse. ## Syntax ```js math.invmod(a, b) ``` ### Parameters Parameter | Type | Description --------- | ---- | ----------- `a` | number | BigNumber | An integer number `b` | number | BigNumber | An integer number ### Returns Type | Description ---- | ----------- number | BigNumber | Returns an integer number where `invmod(a,b)*a ≣ 1 (mod b)` ### Throws Type | Description ---- | ----------- ## Examples ```js math.invmod(8, 12) // returns NaN math.invmod(7, 13) // return 2 math.invmod(15151, 15122) // returns 10429 ``` ## See also [gcd](gcd.md), [xgcd](xgcd.md)