1/( 1+a)= 1/(b-a)+ 1/( 1+b) 1/( 1+b)= 1/( 1+a)- 1/(b-a)

Therefore, (1+b)/(1+a)+(1+a)/(1+b) = (1+b) * (1/(.

=(b+ 1)/(b-a)-(a+ 1)/(b-a)+2 = 3

The second question is -3/4 or 2.

( 1)2x+ 1>0，x>- 1/2，| x-| 2x+ 1 | | = | x-(2x+ 1)| = |-x- 1 | = | x+ 1 | = 3

∵x>- 1/2,∴x+ 1> 1/2>0 ∴x+ 1=3 ∴x=2

(2)2x+ 1