Use the definition of derivatives to find dy/dx for the following:  
(1) y = x^2 -3x + 4  
(2) y = 1/(x-1)
  (3) y = sqrt(x+1)
  (4) y = 1/x^2 
(5) Use the product rule and power rule to find dy/dx if  y = (x^2+x+1) (x^2-1)