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a) 1/1.2 + 1/2.3 + 1/3.4 + .... + 1/x.(x+1) = 499/500
1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + .... + 1/x - 1/x+1 = 499/500
1 - 1/x+1 = 499/500
1/x+1 = 1 - 499/500
1/x+1 = 1/500
x + 1 = 500
x = 500 - 1
x = 499
b) 1/1.3 + 1/3.5 + 1/5.7 + .... + 1/x.(x+2) = 20/41
1/2 . [ 2/1.3 + 2/3.5 + 2/5.7 + ... + 2/x.(x+2) ] = 20/41
1/2 . [ 1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + ... + 1/x - 1/x+2 ] = 20/41
1/2 . [ 1 - 1/x+2 ) = 20/41
1 - 1/x+2 = 20/41 : 1/2
1 - 1/x+2 = 40/41
1/x+2 = 1 - 40/41
1/x+2 = 1/41
x + 2 = 41
x = 41 - 2
x = 39
a) \(x+1,23\div3=1,845\) c) Không rõ
\(x+0,41=1,845\)
\(x=1,845-0,41\)
\(x=1,435\)
b) \(x\times\frac{1}{4}+x\times\frac{1}{5}+x\times2=19,6\) d) \(x+3\frac{1}{2}+20=24\frac{1}{4}\)
\(x\times\left(\frac{1}{4}+\frac{1}{5}+2\right)=19,6\) \(x+\frac{7}{2}+20=\frac{97}{4}\)
\(x\times\frac{49}{20}=19,6\) \(x+\frac{47}{2}=\frac{97}{4}\)
\(x=19,6\div\frac{49}{20}\) \(x=\frac{97}{4}\div\frac{47}{2}\)
\(x=8\) \(x=\frac{97}{94}\)
a) \(x:\frac{1}{2}+\frac{3}{4}=1\frac{19}{20}\)
\(x:\frac{1}{2}+\frac{3}{4}=\frac{39}{20}\)
\(x:\frac{1}{2}=\frac{39}{20}-\frac{3}{4}\)
\(x:\frac{1}{2}=\frac{39}{20}-\frac{15}{20}\)
\(x:\frac{1}{2}=\frac{24}{20}\)
\(x=\frac{24}{20}.\frac{1}{2}\)
\(x=\frac{3}{5}\)
\(x:\frac{1}{2}+\frac{3}{4}=1\frac{19}{20}\)
\(x:\frac{1}{2}=1\frac{19}{20}-\frac{3}{4}\)
\(x:\frac{1}{2}=\frac{39}{20}-\frac{3}{4}\)
\(x:\frac{1}{2}=\frac{39}{20}-\frac{15}{20}\)
\(x:\frac{1}{2}=\frac{24}{20}\)
\(x=\frac{24}{20}\times\frac{1}{2}\)
\(x=\frac{24}{40}\)
\(x=\frac{3}{5}\)
C=1/(2x4)+1/(4x6)+...+1/(18x20)
2C=2/(2x4)+2/(4x6)+...+2/(18x20)
2C=1/2-1/4+1/4-1/6+....-1/20
2C= 1/2- 1/20
2C= 9/20
C= 9/20 x 1/2
C= 9/40
- Quên k auto súc vặc
\(\left(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+...+\frac{1}{18.20}\right).10-x=0\)
\(2\left(\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+...+\frac{2}{18.20}\right).10-x=0\)
\(2\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{18}-\frac{1}{20}\right).10-x=0\)
\(2\left(\frac{1}{2}-\frac{1}{20}\right).10-x=0\)
\(2.\frac{9}{20}.10-x=0\)
\(9-x=0\)
\(x=9-0\)
\(x=9\)
a, X-2/7=1/5
X = 1/5 + 2/7
X = 17/35
b,15/8-X=3/2
X = 15/8-3/2
X = -5/8
c, X x 7/5= 7/20
X = 7/20 : 7/5
X = 1/4
d, 18/25 : X= 9/5
X = 18/25 :9/5
X = 2/5
Nhớ k cho mình nhé! cảm ơn và chúc bạn học tốt :))