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I need to express each difference in simpest form.
This problem is a RAtional expression. To subtract, we have to make sure 
that the denominators are the same. If not, we will find the LCD.
         d^2+3           d - 4 
        _________   -   _______     
         d^2 - 2d          d
         d^2 + 3         d - 4 
        _________   -   _______     LCD is d(d - 2)
         d(d - 2)          d
Make an equivalent expression using the LCD
    d^2 + 3        (d - 4)(d - 2)
   ________   -   _______________
   d(d - 2)           d(d - 2)
  
    d^2 + 3         d^2 - 6d + 8  
   ________   -   _______________  Subtract the numerator, copy the denominator
   d(d - 2)           d(d - 2)
   
      d^2 + 3 - (d^2 - 6d + 8)
     __________________________    
          d (d - 2)
     d^2 + 3 - 1(d^2 - 6d + 8)
     __________________________    
          d (d - 2)
     d^2 + 3 - d^2 + 6d - 8)
     __________________________     Combine like terms
          d (d - 2)
 
          6d - 5
         ________
          d(d -2)
 
and 
         d^2 - 11           d + 1
      ______________  -   _________
       d^2 - 7d +12         d - 4
  
         d^2 - 11           d + 1
      ______________  -   _________  Factor d^2 - 7d +12
      (d - 3)(d - 4)         d - 4
         d^2 - 11         (d + 1)(d - 3)
      ______________  -  ________________  Find equivalent expression using LCD
      (d - 3)(d - 4)      (d - 3)(d - 4)
 
         d^2 - 11         (d^2 - 2d - 3)
      ______________  -  ________________  
      (d - 3)(d - 4)      (d - 3)(d - 4)
  
      d^2 - 11 - (d^2 - 2d - 3)
     ____________________________
            (d - 3)(d - 4)
       d^2 - 11 - 1(d^2 - 2d - 3)
     ____________________________
            (d - 3)(d - 4)
       d^2 - 11 - d^2 + 2d + 3)
     ____________________________  Combine like terms
            (d - 3)(d - 4)
              2d - 8        
          _______________        Factor 2d - 8.
          (d - 3)(d - 4)
 
              2(d - 4)
          _______________    Divide the common factor.
          (d - 3)(d - 4)
              2 
          _______________
          (d - 3) 
           2
        _______
         d - 3