MCD _ _ _ _ _ _ _ _ _ _ _ _ switch

When mcd is on, sums and differences of rational expressions are put on a common denominator. Default is on.

examples:

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

Even with mcd off, rational expressions involving only nu mbers are still put over a common denominator.

Turning mcd 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 mcd 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 mcd is off. This option should therefore be used with some caution. Turning mcd off is most valuable in intermediate parts of a complicated calculation, and should be turned back on for the last stage.