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The `a S` (`calc-solve-for`

) [`solve`

] command rearranges
an equation to solve for a specific variable. An equation is an
expression of the form ‘`L = R`’. For example, the command `a S x`
will rearrange ‘`y = 3x + 6`’ to the form, ‘`x = y/3 - 2`’. If the
input is not an equation, it is treated like an equation of the
form ‘`X = 0`’.

This command also works for inequalities, as in ‘`y < 3x + 6`’.
Some inequalities cannot be solved where the analogous equation could
be; for example, solving
‘`a < b c`’
for ‘`b`’ is impossible
without knowing the sign of ‘`c`’. In this case, `a S` will
produce the result
‘`b != a/c`’
(using the not-equal-to operator) to signify that the direction of the
inequality is now unknown. The inequality
‘`a <= b c`’
is not even partially solved. See Declarations, for a way to tell
Calc that the signs of the variables in a formula are in fact known.

Two useful commands for working with the result of `a S` are
`a .` (see Logical Operations), which converts ‘`x = y/3 - 2`’
to ‘`y/3 - 2`’, and `s l` (see The Let Command) which evaluates
another formula with ‘`x`’ set equal to ‘`y/3 - 2`’.