# Function usolve Solves the linear equation system by backward substitution. Matrix must be an upper triangular matrix. `U * x = b` ## Syntax ```js math.usolve(U, b) ``` ### Parameters Parameter | Type | Description --------- | ---- | ----------- `U` | Matrix, Array | A N x N matrix or array (U) `b` | Matrix, Array | A column vector with the b values ### Returns Type | Description ---- | ----------- DenseMatrix | Array | A column vector with the linear system solution (x) ## Examples ```js const a = [[-2, 3], [2, 1]] const b = [11, 9] const x = usolve(a, b) // [[8], [9]] ``` ## See also [lup](lup.md), [slu](slu.md), [usolve](usolve.md), [lusolve](lusolve.md)