The simplify command is used to apply simplification rules to an expression.

The Error, (in simplify/do) invalid simplification command message occurs when arguments passed to simplify do not comply with a valid calling sequence.

Example 1

In this instance, the arguments do not match any of the valid calling sequences of simplify.

Solution 1:

Enclose the equation $x\=y$ in a set.

Solution 2:

For a direct substitution, you can also use the eval command.

Example 2

Here, $\mathrm{eqn}$ provides a side relation that should be used when simplifying the expression $\mathrm{expr}$. The side relations passed to simplify must be a set or list of equations. For more information on side relations, see simplify/siderels.

Solution:
Enclose the equation in a set.