Q= 100+98+96+...+4+2-97-95-...-3-1

R =|-129|-119+|2-31|

(1-1/2)(1-1/3)(1-1/4)...(1-1/20)=1/2.2/3.3/4...19/20=1/20

1 like nha

Luc ta nhan thi gian uoc ca tu va mau nen chi con lai tu la 1 va mau la 20 nen =1/20

\(A\left(x\right)=x^{99}-100x^{98}+....+100x-1\)

\(=x^{99}-99x^{99}+99x^{98}-99x^{97}+...+99x+x-1\)

\(=x^{98}\left(x-99\right)-x^{97}\left(x-99\right)+x^{96}\left(x-99\right)+..+x\left(x-99\right)-x-1\) 

thay \(A\left(x\right)=99\)  ta có: 

\(A\left(99\right)=99^{98}\left(99-99\right)-99^{97}\left(99-99\right)+...+99\left(99-99\right)-99-1\)

\(=99^{98}.0-99^{97}.0+99^{96}.0-...+99.0-99-1\)

\(=0-0+0-...-0+99-1\)

\(=99-1\)

\(=98\)