;-;

\(S=\dfrac{1}{50}+\dfrac{1}{51}+\dfrac{1}{52}+...+\dfrac{1}{98}+\dfrac{1}{99}\)

\(S=\dfrac{1}{50}>100\)    \(\dfrac{1}{51}>100\)   \(\dfrac{1}{52}>100\)   \(....\)   \(\dfrac{1}{98}>100\)    \(\dfrac{1}{99}>100\)

\(\Rightarrow S>\dfrac{1}{100}+\dfrac{1}{100}+\dfrac{1}{100}+...+\dfrac{1}{100}+\dfrac{1}{100}\\ \) {50 số 100}

\(S>50\cdot\dfrac{1}{100}=\dfrac{1}{2}\)

\(S>\dfrac{1}{2}\)

co ai tra loi ko

Bài này thầy Chung dạy rồi mà

a)Ta có:

 A= 1/1.2+1/2.3+1/3.4+.....+1/99.100

=1-1/2+1/2-1/3+...+1/99-1/100

=1-1/100

=99/100

b)Ta có:

B= 1/11+1/12+1/13+1/14+1/15+...+1/50

=(1/11+1/50)+(1/12+1/49)+...+(1/30+1/31)

=61/11.50+61/12.49+...+61/30.31

=61.(1/11.50+1/12.49+...+1/30.31)

Mình xin lỗi chỉ làm được đến đây vì dạng tính B mình không tốt lắm ◕◡◕

\(B=\left(\frac{1}{11}+\frac{1}{12}+...+\frac{1}{30}\right)+\left(\frac{1}{31}+\frac{1}{32}+...+\frac{1}{50}\right)>\left(\frac{1}{30}+\frac{1}{30}+...+\frac{1}{30}\right)+\left(\frac{1}{50}+\frac{1}{50}+...+\frac{1}{50}\right)\)=> \(B>\frac{20}{30}+\frac{20}{50}=\frac{2}{3}+\frac{2}{5}=\frac{16}{15}>1\)

mà \(A=\frac{99}{100}

ssssssssss

(2 x X - 1)mũ 3 = (2 x X - 2)mũ 2

B=1/50+1/51+1/52+...+1/99

Ta có: 1/50=1/50

          1/51<1/50

          1/52<1/50

          ..............

          1/99<1/50

1/50+1/51+1/52+...+1/99<1/50+1/50+1/50+...+1/50(50 phân số 1/50)

B<1