a/ => | x - 7 | = 5 + x
TH1: x - 7 = 5 + x => 0x = 12 (VN)
TH2: x - 7 = - 5 - x => 2x = 2 => x = 1
Vậy x = 1
b/ \(\Rightarrow\int^{x-2015\ge0}_{x+2015<0}\) \(\Rightarrow\int^{x\ge2015}_{x<-2015}\) (vô lí)
hoặc \(\int^{x-2015<0}_{x+2015\ge0}\) \(\Rightarrow\int^{x<2015}_{x\ge-2015}\) \(\Rightarrow-2015\le x<2015\)