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Least common denominator z/(z+9)^2-z/(z^2-81)

An expression to simplify:

The solution

You have entered [src]
   z          z   
-------- - -------
       2    2     
(z + 9)    z  - 81
$$- \frac{z}{z^{2} - 81} + \frac{z}{\left(z + 9\right)^{2}}$$
z/(z + 9)^2 - z/(z^2 - 81)
General simplification [src]
         -18*z         
-----------------------
        3             2
-729 + z  - 81*z + 9*z 
$$- \frac{18 z}{z^{3} + 9 z^{2} - 81 z - 729}$$
-18*z/(-729 + z^3 - 81*z + 9*z^2)
Fraction decomposition [src]
1/(2*(9 + z)) - 9/(9 + z)^2 - 1/(2*(-9 + z))
$$\frac{1}{2 \left(z + 9\right)} - \frac{9}{\left(z + 9\right)^{2}} - \frac{1}{2 \left(z - 9\right)}$$
    1          9           1     
--------- - -------- - ----------
2*(9 + z)          2   2*(-9 + z)
            (9 + z)              
Common denominator [src]
         -18*z         
-----------------------
        3             2
-729 + z  - 81*z + 9*z 
$$- \frac{18 z}{z^{3} + 9 z^{2} - 81 z - 729}$$
-18*z/(-729 + z^3 - 81*z + 9*z^2)
Combinatorics [src]
      -18*z      
-----------------
                2
(-9 + z)*(9 + z) 
$$- \frac{18 z}{\left(z - 9\right) \left(z + 9\right)^{2}}$$
-18*z/((-9 + z)*(9 + z)^2)
Numerical answer [src]
-z/(-81.0 + z^2) + 0.0123456790123457*z/(1 + 0.111111111111111*z)^2
-z/(-81.0 + z^2) + 0.0123456790123457*z/(1 + 0.111111111111111*z)^2
Combining rational expressions [src]
  /       2          2\
z*\-81 + z  - (9 + z) /
-----------------------
  /       2\        2  
  \-81 + z /*(9 + z)   
$$\frac{z \left(z^{2} - \left(z + 9\right)^{2} - 81\right)}{\left(z + 9\right)^{2} \left(z^{2} - 81\right)}$$
z*(-81 + z^2 - (9 + z)^2)/((-81 + z^2)*(9 + z)^2)
Rational denominator [src]
  /       2\            2
z*\-81 + z / - z*(9 + z) 
-------------------------
   /       2\        2   
   \-81 + z /*(9 + z)    
$$\frac{- z \left(z + 9\right)^{2} + z \left(z^{2} - 81\right)}{\left(z + 9\right)^{2} \left(z^{2} - 81\right)}$$
(z*(-81 + z^2) - z*(9 + z)^2)/((-81 + z^2)*(9 + z)^2)