M= \(\dfrac{1}{(x+1)(x+2)}\)+ \(\dfrac{1}{(x+2)(x+3)}\)+ \(\dfrac{1}{(x+3)(x+4)}\)+ \(\dfrac{1}{(x+4)(x+5)}\)+ \(\dfrac{1}{x+5}\)

M= \(\dfrac{1}{x+1}\)- \(\dfrac{1}{x+2}\)+ \(\dfrac{1}{x+2}\)- \(\dfrac{1}{x+3}\)+ \(\dfrac{1}{x+3}\)- \(\dfrac{1}{x+4}\)+ \(\dfrac{1}{x+4}\)+ \(\dfrac{1}{x+5}\)

M= \(\dfrac{1}{x+1} + \dfrac{1}{x+5}\)

M= \(\dfrac{x+5}{(x+1)(x+5)} + \dfrac{x+1}{(x+1)(x+5)} \)

M= \(\dfrac{x+5+x+1}{(x+1)(x+5)}\)

M= \(\dfrac{2x+6}{(x+1)(x+5)}\)

M= \(\dfrac{2(x+3)}{(x+1)(x+5)}\)

1, CMR:
x+ y+ z = -3 thì:

(x+ 1)³+ (y+1)³+ (z+1)³ = 3(x+1)(y+1)(z+1)

Tìm tập hợp tất cả các giá trị của tham số thực m để phương trình  9 1 - x + 2 ( m - 1 ) 3 1 - x + 1 = 0 có 2 nghiệm phân biệt.

A. m > 1

B. m < -1

C. m < 0

D. -1 < m < 0