\(S=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{40.43}+\frac{3}{43.46}\)

\(S=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{40}-\frac{1}{43}+\frac{1}{43}-\frac{1}{46}\)

\(S=1-\frac{1}{46}< 1\)

Chứng tỏ S < 1

Ủng hộ mk nha ^_^

S = \(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+......+\frac{3}{43.46}\)

  \(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+.....+\frac{1}{43}-\frac{1}{46}\)

   \(=1-\frac{1}{46}=\frac{45}{46}< 1\)

S=1-1/4 + 1/4 - 1/7 +1/7 - 1/10 +...+ 1/40 - 1/43 +1/43 -1/46

  = 1-1/46 < 1 (ĐPCM)

= 1 -1/4 +1/4 -1/7 +1/7 -1/10+...+1/40 -1/43 +1/43 -1/46

= 1 -1/46

= 45/46

\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{40.43}+\frac{3}{43.46}\)

\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{40}-\frac{1}{43}+\frac{1}{43}-\frac{1}{46}\)

\(=1-\frac{1}{46}\)

\(=\frac{45}{46}\)

_Chúc bạn học tốt_

3/1×4 + 3/4×7 + 3/7×10 +...+ 3/40×43 + 3/43*46

=1-1/4+1/4-1/7+1/7-1/10+...+1/40-1/43+1/43-1/46

=1-1/46

=46/46-1/46

=45/46

Chữa bài lâu rồi mà chẳng có ai chả lời chỉ

\(S=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{40.43}+\frac{3}{43.46}\) < 1

\(S=3\left(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+...+\frac{1}{40.43}+\frac{1}{43.46}\right)\)

\(S=3.\frac{1}{3}\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{40}-\frac{1}{43}+\frac{1}{43}-\frac{1}{46}\right)\)

\(\Rightarrow S=1-\frac{1}{46}\Rightarrow S< 1\left(đpcm\right)\)

\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{40.43}+\frac{3}{43.46}\)

= \(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{40}-\frac{1}{43}+\frac{1}{43}-\frac{1}{46}\)

= \(1-\frac{1}{46}< 1\)

\(\Rightarrow S< 1\left(đpcm\right)\)

\(\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+....+\frac{3}{40\cdot43}\)

\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+....+\frac{1}{40}-\frac{1}{43}\)

\(=1-\frac{1}{43}=\frac{42}{43}\)

=42/32

Điểm trung bình thi đua cả năm là;

\(\dfrac{6+7+7+8+1+2+10+8+9}{9}\simeq6,4\)

Ta có: \(\frac{3}{1.4}+\frac{3}{4.7}+......+\frac{3}{40.43}+\frac{3}{43.46}\)

\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+....+\frac{1}{40}-\frac{1}{43}+\frac{1}{43}-\frac{1}{46}\)

\(=1-\frac{1}{46}\)

Vì \(\frac{1}{46}>0\Rightarrow1-\frac{1}{46}< 1\)

Vậy \(\frac{3}{1.4}+\frac{3}{4.7}+....+\frac{3}{43.46}< 1\)

Câu 22: Hãy sắp xếp số sau theo thứ tự tăng dần: -3; +4; 7; -7; 0; -1.
A. – 7; - 3 ; - 1; 0 ; + 4 ; 7.     B. 7; +4; 0; -1; -3; -7.
C.7; -7; +4; -3; -1; 0.              D. 0; -1; -3; +4; - 7; 7.
Câu 23: Liệt kê các phần tử của mỗi tập hợp: P = { x ε Z ǀ -2 ≤ x < 4}
A. P = { -2; -1; 0; 1; 2; 3; 4}.          B. P = {-1; 0; 1; 2; 3; 4}.
C. P = {-1; 0; 1; 2; 3}.                      D. P = {-2; -1; 0; 1; 2; 3}.

22-a

23-a

\(\frac{3}{1.4}+\frac{3}{4.7}+...+\frac{3}{40.43}+\frac{3}{43.46}\)

\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{40}-\frac{1}{43}+\frac{1}{43}-\frac{1}{46}\)

\(=1-\frac{1}{46}< 1\)

Vậy \(S< 1\)

Chúc bạn học tốt !!! 

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