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- 22.32.5:22.3-32=3.5-32=15-9=6
- 2.52-22.32:32=2.(52-2)=2.(25-2)=46
3. 33.19-33.12=33.(19-12)=33.7=189
4. 3.52-16:22=3.52-24:22=3.25-4=75-4=71
Ta có 1/22<1/1.2
1/32<1/2.3
1/42<1/3.4
................
1/8²<1/7.8
=>B<1/1.2+1/2.3+1/3.4+...+1/7.8
=>B<1-1/2+1/2-1/3+1/3-1/4+...+1/7-1/8
=>B<1-1/8
Vậy B < 1
\(A=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{10^2}\)
\(< \frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)
\(=\frac{2-1}{1.2}+\frac{3-2}{2.3}+\frac{4-3}{3.4}+...+\frac{10-9}{9.10}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(=1-\frac{1}{10}< 1\)
\(A=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{10^2}\\ A< \frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{9\times10}\\ A< 1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}=1-\frac{1}{10}\\ A< \frac{9}{10}< 1\Rightarrow A< 1\)
b=1/22+1/32+1/42+...+1/82<1/1.2+1/2.3+1/3.4+......+1/7.8
b=1-1/2+1/2-1/3+1/3-1/4+....+1/7-1/8
b=1-1/8
b=7/8
<=>b<1
k cho mink nha
b=1/22+1/32+1/42+...+1/82<1/1.2+1/2.3+1/3.4+......+1/7.8
b=1-1/2+1/2-1/3+1/3-1/4+....+1/7-1/8
b=1-1/8
b=7/8
<=>b<1
owo