Tính nhanh
54×27×2
Các bạn giúp mình nha
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a) 4/ 3x7 + 4/7x11+ 4/11x15+...+ 4/107x111
=1/3-1/7+ 1/7-1/11+ 1/11- 1/15+...+1/107 - 1/111
= 1/3-1/111
=12/37
\(b,\frac{3^2}{8\cdot11}+\frac{3^2}{11\cdot14}+\frac{3^2}{14\cdot17}+...+\frac{3^2}{197\cdot200}\)
\(=3\left(\frac{3}{8\cdot11}+\frac{3}{11\cdot14}+\frac{3}{14\cdot17}+...+\frac{3}{197\cdot200}\right)\)
\(=3\left(\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}+...+\frac{1}{197}-\frac{1}{200}\right)\)
\(=3\left(\frac{1}{8}-\frac{1}{200}\right)\)
\(=3\cdot\frac{3}{25}=\frac{9}{25}\)
45.(x - 3/4) - 1/2.(x + 2/5) = 3
<=> 1024.(x - 3/4) - 1/2.(x + 2/5) = 3
<=> 1024.(x - 3/4).2 - (x + 2/5).2 = 3.2
<=> 2048.(x - 3/4) - (x - 2/5) = 6
<=> 2047x - 7678/5 = 6
<=> 2047x = 6 + 7678/5
<=> 2047x = 7708/5
<=> x = 7708/5 : 2047
<=> x = 7708/10235
=> x = 7708/10235
a) 1/1.2 + 1/2.3 + ... + 1/2019.2020
= 1 - 1/2 + 1/2 - 1/3 + ... + 1/2019 - 1/2020
= 1 - 1/2020
= 2019/2020
b) 1/1.4 + 1/4.7 + ... + 1/100.103
= 1/3.(1 - 1/4 + 1/4 - 1/7 + ... + 1/100 - 1/103)
= 1/3.(1 - 1/103)
= 1/3.102/103
= 34/103
\(a,\frac{1}{1.2}+\frac{1}{2.3}+....+\frac{1}{2019.2020}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+....+\frac{1}{2019}-\frac{1}{2020}\)
\(=1-\frac{1}{2020}=\frac{2019}{2020}\)
\(b,\frac{1}{1.4}+\frac{1}{4.7}+....+\frac{1}{100.103}\)
\(=\frac{1}{3}\left(\frac{3}{1.4}+\frac{1}{4.7}+....+\frac{1}{100.103}\right)\)
\(=\frac{1}{3}.\left(1-\frac{1}{103}\right)=\frac{1}{3}.\frac{102}{103}=\frac{34}{103}\)
(x - 1)2 + 2.(1 - 2)2 = 12
=> (x - 1)2 + 2.(-1)2 = 12
=> (x - 1)2 = 12 - 2
=> (x - 1)2 = 10
=> \(\orbr{\begin{cases}x-1=\sqrt{10}\\x-1=-\sqrt{10}\end{cases}}\)
=> \(\orbr{\begin{cases}x=1+\sqrt{10}\\x=1-\sqrt{10}\end{cases}}\)
Vậy....
Bài giải
Ta có :
\(\frac{4x+4}{x-2}=\frac{4\left(x-2\right)+8+4}{x-2}=\frac{4\left(x-2\right)}{x-2}+\frac{8+4}{x-2}=4+\frac{12}{x-2}\)
\(4x+4\text{ }⋮\text{ }x-2\) khi \(12\text{ }⋮\text{ }x-2\)
\(\Leftrightarrow\) \(x-2\inƯ\left(12\right)\)
Ta có bảng :
\(x-2\) | \(-1\) | \(1\) | \(-2\) | \(2\) | \(-3\) | \(3\) | \(-4\) | \(4\) | \(-6\) | \(6\) | \(-12\) | \(12\) |
\(x\) | \(1\) | \(3\) | \(0\) | \(4\) | \(-1\) | \(5\) | \(-2\) | \(6\) | \(-4\) | \(8\) | \(-10\) | \(14\) |
\(\Rightarrow\text{ }x\in\left\{1\text{ ; }3\text{ ; }0\text{ ; }4\text{ ; }-1\text{ }5\text{ ; }-2\text{ ; }6\text{ ; }-4\text{ ; }8\text{ ; }-10\text{ ; }14\right\}\)
Ta có :
\(4x+4=4(x-2)+12 \)
\(\Rightarrow 4(x-2)+12 \vdots x-2\)
\(4(x-2) \vdots x-2 \Rightarrow 12\vdots x-2 \)
x-2 | 1 | -1 | 2 | -2 | 3 | -3 | 4 | -4 | 6 | -6 | 12 | -12 |
x | 3 | 1 | 4 | 0 | 5 | -1 | 6 | -2 | 8 | -4 | 14 | -10 |
=2916
=2916 nha bạn
Hội con 🐄 chúc bạn học tốt!!!