Cho B=1/1^2+1/3^2+1/4^2+.._+1/2021.2023. Chứng minh rằng 29/62
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Cho B= 1/2^2+1/3^2+1/4^2+...+1/30^2. Chứng minh rằng 29/62
Cho B= 1/2^2+1/3^2+1/4^2+...+1/30^2. Chứng minh rằng 29/62
\(B>\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{30.31}\)
\(B>\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{30}-\dfrac{1}{31}\)
\(B>\dfrac{1}{2}-\dfrac{1}{31}=\dfrac{29}{62}\left(đpcm\right)\)
Đúng 1
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Cho B= 1/2^2+1/3^2+1/4^2+...+1/30^2. Chứng minh rằng 29/62
\(B>\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{30.31}\)
\(B>\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{30}-\dfrac{1}{31}\)
\(B>\dfrac{1}{2}-\dfrac{1}{31}=\dfrac{29}{62}\left(đpcm\right)\)
Đúng 3
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Chứng minh rằng 3 < 1+1/2+1/3+1/4+1/5+...+1/62+1/63<6
cho:
a) A= 2+\(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+....+\frac{1}{62}+\frac{1}{63}+\frac{1}{64}+\frac{1}{65}+\frac{1}{66}+\frac{1}{67}\)
chứng minh rằng A>5
b) B= \(\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{89^2}+\frac{1}{90^2}\)
chứng minh rằng \(\frac{40}{91}\)<B<1
Chứng minh rằng:
1+a+a^2+a^3+...+a^62+a^63=(1+a)(1+a^2)(1+a^4)...(1+a^32)
Chứng minh rằng M<6 biết :
M =1 + 1/2 + 1/3 + 1/4 + ... + 1/62 + 1/63
ai trả lời nhanh và đúng nhất cho ít nhất 3 Tick nhé ^_^
Cho \(A=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{9^2}\)
Chứng minh rằng: \(\frac{29}{60}< A< \frac{2}{3}\)
Ta có :
\(A=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{9^2}\)
\(\Rightarrow A>\frac{1}{2^2}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\)
\(\Leftrightarrow A>\frac{1}{2^2}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{10}\)
\(=\frac{1}{2^2}+\frac{1}{3}-\frac{1}{10}=\frac{29}{60}\left(1\right)\)
Lại có :
\(A< \frac{1}{2^2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{8.9}\)
\(\Leftrightarrow A< \frac{1}{2^2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}\)
\(=\frac{1}{2^2}+\frac{1}{2}-\frac{1}{9}=\frac{23}{36}\left(2\right)\)
Mà \(\frac{23}{36}< \frac{24}{36}=\frac{2}{3}\left(3\right)\)
Từ (1), (2) và (3) suy ra \(\frac{29}{60}< A< \frac{2}{3}\)
Chứng minh rằng : 1/5+1/4+1/28+1/44+1/62+1/84+1/97 < 1/2