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a/
\(1\frac{1}{2}x1\frac{1}{3}x1\frac{1}{4}x1\frac{1}{5}x1\frac{1}{6}=\frac{3}{2}x\frac{4}{3}x\frac{5}{4}x\frac{6}{5}x\frac{7}{6}=\frac{7}{2}=3\frac{1}{2}\)
b/
x=0; y=5
A.1/2x3 +1/3x4 +1/4x5+...+1/99x100
=1/2 -1/3 +1/3-1/4+1/4-1/5+...+1/99-1/100
=1/2-1/100
=49/100
3/4 x 8/9 x 15/16 x ... x 99/100 x 120/121 = 3 x 8 x 15 x 99 x 120/ 4 x 9 x 16 x 100 x 121
= ( 1 x 3 ) x ( 2 x 4 ) x ( 3 x 5 ) x ... x ( 9 x 11 ) x ( 10 x 12 ) / ( 2 x 2 ) x ( 3 x 3 ) x ( 4 x 4 ) x ... x ( 10 x 10 ) x ( 11 x 11 )
= ( 1 x 2 x 3 x ... x 10 ) x ( 3 x 4 x 5 x ... x 12 ) / ( 2 x 3 x ... x 11 ) x ( 2 x 3 x ... x 11 ) = 12/11x2 = 6/11
\(\left(1+x\right)+\left(2+x\right)+\left(3+x\right)+\)\(\left(4+x\right)+\left(5+x\right)=10\times5\)
\(\left(1+2+3+4+5\right)+\left(x+x+x+x+x\right)=50\)
\(15+5x=50\)
\(5x=35\)
\(x=7\)
Vậy \(x=7\)
\(\left(1+x\right)+\left(2+x\right)+\left(3+x\right)+\left(4+x\right)+\left(5+x\right)=10\times5\)
\(\Rightarrow1+x+2+x+3+x+4+x+5+x=50\)
\(\Rightarrow\left(1+2+3+4+5\right)+\left(x+x+x+x+x\right)=50\)
\(\Rightarrow15+5x=50\)
\(\Rightarrow5x=50-15\)
\(\Rightarrow5x=35\)
\(\Rightarrow x=35:5\)
\(\Rightarrow x=7\).
1 + 1 = 2
2 + 3= 5
6 + 6 = 12
Tìm x:
X + 3,68 = 4,035
X = 4,035 - 3,68
X = 0,355
5,0165 : X = 5
X = 5,0165 : 5
X = 1,0033
Ủng hộ nha! :)
Bài 1 :
1 + 1 = 2
2 + 3 = 5
6 + 6 = 12
Bài 2 :
x + 3,68 = 4,035
x = 4,035 - 3,68
x = 0,35
5,0165 : x = 5
x = 5,0165 : 5
x = 1.0033
B1 Nhân biểu tthức trên với 1/2 được
1/6+1/12/+1/20+....+1/110=1/2×3+1/3×4+.....+1/10×11
=1/2-1/3+1/3-1/4+.....+1/10-1/11=1/2-1/11=9/22
B2
B.1/1×2+1/2×3+.....+1/99×100=1-1/2 +1/2-1/3+....+1/99-1/100=1-1/100=99/100
Phần a sai đề phải llà1/2×4+1/4×6+.....+1/8×10 mới làm đc nhé
a) \(\frac{1}{3}-\frac{2}{x}=\frac{1}{6}\)
=> \(\frac{2}{x}=\frac{1}{3}-\frac{1}{6}\)
=> \(\frac{2}{x}=\frac{1}{6}\)
\(\Rightarrow x=12\)
Vậy x = 12
b) \(\frac{x-1}{2}=\frac{3}{4}\)
\(\Rightarrow\left(x-1\right).4=2.3\)
=> 4x - 4 = 6
=> 4.(x-1) = 6
=> x-1 = 6:4 = 1,5
=> x = 1,5 + 1
=> x = 2,5
Vậy x = 2,5
\(\left(1-\frac{1}{3}\right)x\left(1-\frac{1}{4}\right)x...x\left(1-\frac{1}{2014}\right)\)
A = \(\frac{2}{3}x\frac{3}{4}x\frac{4}{5}x...x\frac{2012}{2013}x\frac{2013}{2014}\)
A = \(\frac{2x3x4x...x2012x2013}{3x4x5x...x2013x2014}\)
a = \(\frac{2}{2014}=\frac{1}{1007}\)
Ta có: \(1+\dfrac{1}{3}+\dfrac{1}{6}+...+\dfrac{2}{x\left(x+1\right)}=\dfrac{4044}{2023}\)
=>\(\dfrac{2}{2}+\dfrac{2}{6}+\dfrac{2}{12}+...+\dfrac{2}{x\cdot\left(x+1\right)}=\dfrac{4044}{2023}\)
=>\(\dfrac{1}{2}+\dfrac{1}{6}+...+\dfrac{1}{x\left(x+1\right)}=\dfrac{2022}{2023}\)
=>\(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{x}-\dfrac{1}{x+1}=\dfrac{2022}{2023}\)
=>\(1-\dfrac{1}{x+1}=\dfrac{2022}{2023}\)
=>\(\dfrac{1}{x+1}=1-\dfrac{2022}{2023}=\dfrac{1}{2023}\)
=>x+1=2023
=>x=2022
Đề có đúng không ạ ?