35.(72-135) - 135.(72-35)= 35.72 - 35.135 - 135.72 - 135.35

                                   = 35.72 - 135.72 - [(35.135) - (135.35)]

                                   =72.(35-135) -0

                                   =72.(-100)

                                   =(-7200)

\(x+\left(x+1\right)+\left(x+2\right)+\left(x+3\right)+\left(x+4\right)+........+\left(x+2019\right)=2019\)

\(\Rightarrow\left(x+x+x+x+.........+x+x+\right)+\left(1+2+3+4+........+2018+2019\right)=2019\)

\(\Rightarrow2020x+2039190=2019\)(Tự làm tiếp )

no i don't think i'll

ta có :

\(1-\frac{2}{2.3}=\frac{2.3-2}{2.3}=\frac{1.2}{2.3}\)

tương tự : \(1-\frac{2}{3.4}=\frac{2.3}{3.4},....,1-\frac{2}{2020.2021}=\frac{2019.2020}{2020.2021}\)

Vậy \(S=\frac{1.2}{2.3}.\frac{2.3}{3.4}.....\frac{2019.2020}{2020.2021}=\frac{1.\left(2.3...2019\right)^2.2020}{2.\left(3.4....2020\right)^2.2021}=\frac{2}{2020.2021}\)

\(a)-\frac{5}{19}+\frac{3}{19}< \frac{x}{19}< \frac{13}{19}+-\frac{11}{19}\)

\(\Rightarrow\frac{-5+3}{19}< \frac{x}{19}< \frac{13+(-11)}{19}\)

\(\Rightarrow-\frac{2}{19}< \frac{x}{19}< \frac{2}{19}\)

Tìm x đi rồi ra được kết quả