## Tip 27. Trust but verify

Certainly this tip concerns not only to Mathcad but also to all software
for solution of mathematical problems. So if you get an answer, don’t be lazy
to *verify* it*.* The roots of our
system (see tip 24
and tip 26) are substituted in the initial
equations in the fig. 27.
For it the matrix with the roots from Mathcad-document, which illustrates tip 26, is put down in the variable Roots. Then the pairs of values from lines of the matrix Roots are carried to the variables x and y. In their
turns they are substituted in left parts of the algebraic equations of the test
system. It is possible to predetermine about quality of the solution using the
analysis of *residual** *(it equals 5.627.10^{-4
}for six root).