2^x+1.3+15=39
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IA
9 tháng 6 2018
\(x\div6\times7,2+1,3\times x+x\div2+15=19,95\)
\(\Leftrightarrow x\times\frac{1}{6}\times7,2+1,3\times x+x\times\frac{1}{2}=19,95-15\)
\(\Leftrightarrow x\times1,2+x\times1,3+x\times\frac{1}{2}=4,95\)
\(\Leftrightarrow x\times\left(1,2+1,3+\frac{1}{2}\right)=4,95\)
\(\Leftrightarrow x\times3=4,95\)
\(\Leftrightarrow x=4,95\div3\)
\(\Leftrightarrow x=1,65\)
Vậy x = 1,65
DX
0
ND
Nguyễn Đức Trí
VIP
3 tháng 8 2023
\(\dfrac{5}{8}x-\dfrac{1}{3}x-\dfrac{1}{6}x=15\)
\(\Rightarrow x\left(\dfrac{5}{8}-\dfrac{1}{3}-\dfrac{1}{6}\right)=15\)
\(\Rightarrow x\left(\dfrac{15}{24}-\dfrac{8}{24}-\dfrac{4}{24}\right)=15\)
\(\Rightarrow x.\dfrac{3}{24}=15\)
\(\Rightarrow x.\dfrac{1}{8}=15\Rightarrow x=15:\dfrac{1}{8}=15.\dfrac{8}{1}=120\)
9 tháng 2 2017
Đề: \(\frac{\left(x-1\right)}{2}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{13}-\frac{1}{15}\right)=\frac{3}{5x}-\frac{7}{15}\)
\(\Leftrightarrow\frac{\left(x-1\right)}{2}\left(1-\frac{1}{15}\right)=\frac{3}{5x}-\frac{7}{15}\)
\(\Leftrightarrow\frac{\left(x-1\right)}{2}.\frac{14}{15}=\frac{3}{5x}-\frac{7}{15}\Leftrightarrow\frac{7\left(x-1\right)+7}{3}=\frac{3}{x}\)
\(\Leftrightarrow\frac{7x}{3}=\frac{3}{x}\Leftrightarrow\orbr{\begin{cases}x=\frac{\sqrt{7}}{3}\\x=-\frac{\sqrt{7}}{3}\end{cases}}\)
3 tháng 5 2015
mình làm được bài tìm x
x.(2/1.3+2/3.5+2/5.7+...+2/97.99)-x=-100/99
x.(1-1/3+1/3-1/4+1/4-1/5+1/5+...+1/97-1/97-1/99)-x=-100/99
x.(1-1/99)-x=-100/99
x.98/99-x=-100/99
x.98/99=-100/99+x
x.x=-100/99-98/99
2x=-198/99
x=-198/99/2
x=-1
NA
Ngoc Anh Thai
Giáo viên
11 tháng 4 2021
Em xem lại đề câu B nhé\(B=\dfrac{3}{2}+\dfrac{3}{6}+\dfrac{3}{12}+\dfrac{3}{20}+...+\dfrac{3}{\left(n-1\right).n}\\ =3.\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{\left(n-1\right).n}\right)\\ =3.\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{n-1}-\dfrac{1}{n}\right)=3.\left(1-\dfrac{1}{n}\right)=3.\dfrac{n-1}{n}=3-\dfrac{3}{n}.\)
\(C=\dfrac{2}{1.3}+\dfrac{2}{3.5}+...+\dfrac{2}{30.32}\\ =1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+...+\dfrac{1}{30}-\dfrac{1}{32}\\ =1-\dfrac{1}{32}=\dfrac{31}{32}.\)
\(D=\dfrac{1}{2}.\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+...+\dfrac{1}{n+1}-\dfrac{1}{n+3}\right)\\ =\dfrac{1}{2}.\left(1-\dfrac{1}{n+3}\right)=\dfrac{1}{2}.\dfrac{n+2}{n+3}.\)
RA
6
H
6 tháng 5 2019
\(a,\left(\frac{15}{10}x+25\right):\frac{2}{3}=60\)
\(\Rightarrow\frac{15}{10}x+25=60.\frac{2}{3}\)
\(\Rightarrow\frac{15}{10}x+25=40\)
\(\Rightarrow\frac{15}{10}x=40-25\)
\(\Rightarrow\frac{15}{10}x=15\)
\(\Rightarrow x=15:\frac{15}{10}\)
\(\Rightarrow x=15.\frac{10}{15}\)
\(\Rightarrow x=10\)
NN
Nguyễn Ngọc Anh Minh
CTVHS
VIP
14 tháng 10 2023
\(M=\dfrac{2^2.3^2.4^2.....20^2}{1.3.2.4.3.5.4.6.5.7.6.8.7.9....19.21}=\)
\(=\dfrac{2^2.3^2.4^2....20^2}{1.2.3^2.4^2....19^2.20.21}=\dfrac{2.20}{21}=\dfrac{40}{21}\)
\(N=\dfrac{1}{2}.\dfrac{2}{3}.\dfrac{3}{4}.....\dfrac{10}{11}=\dfrac{1}{11}\)
\(\Leftrightarrow2^{x+1}=8\)
=>x+1=3
hay x=2