<A NAME=MCD>
<TITLE>MCD</TITLE></A>
<b><a href=r37_idx.html>INDEX</a></b><p><p>
<B>MCD</B> _ _ _ _ _ _ _ _ _ _ _ _ <B>switch</B><P>
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When <em>mcd</em> is on, sums and differences of rational expressions are put
on a common denominator. Default is <em>on</em>.
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examples: </H3>
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a/(x+1) + b/5;
5*A + B*X + B
-------------
5*(X + 1)
off mcd;
a/(x+1) + b/5;
-1
(X + 1) *A + 1/5*B
1/6 + 1/7;
13/42
</TT></PRE><P>Even with <em>mcd</em> off, rational expressions involving only nu
mbers are still
put over a common denominator.
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Turning <em>mcd</em> off is useful when explicit negative powers are needed,
or if no greatest common divisor calculations are desired, or when
differentiating complicated rational expressions. Results when <em>mcd</em>
is off are no longer in canonical form, and expressions equivalent to zero
may not simplify to 0. Some operations, such as factoring cannot be done
while <em>mcd</em> is off. This option should therefore be used with some
caution. Turning <em>mcd</em> off is most valuable in intermediate parts of
a complicated calculation, and should be turned back on for the last stage.
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