Cho P=x/x-4 + 1/căn x -2 + 1/căn x +2 Q=căn x -2/căn x -3 a)chứng minh P=căn x/căn x -2 b)vs x thuộc N . tìm max K=Q.(P-1)

P=$\frac{x}{x-4}$ + $\frac{1}{√x -2}$ +$\frac{1}{√x +2}$

<=> $\frac{x+√x +2+√x -2}{(√x+2)(√x−2)}$ 

<=> $\frac{x+2√x}{(√x+2)(√x−2)}$ <=> $\frac{√x(√x+2)}{√x+2)(√x−2)}$ <=>$\frac{√ x }{√ x − 2 }$