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\(\dfrac{3x}{2.5}+\dfrac{3x}{5.8}+\dfrac{3x}{8.11}+\dfrac{3x}{11.14}=\dfrac{1}{21}\)
\(\Rightarrow x\left(\dfrac{3}{2.5}+\dfrac{3}{5.8}+\dfrac{3}{8.11}+\dfrac{3}{11.14}\right)=\dfrac{1}{21}\)
\(\Rightarrow x\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{14}\right)=\dfrac{1}{21}\)
\(\Rightarrow x\left(\dfrac{1}{2}-\dfrac{1}{14}\right)=\dfrac{1}{21}\)
\(\Rightarrow x.\dfrac{3}{7}=\dfrac{1}{21}\)
\(\Rightarrow x=\dfrac{1}{21}.\dfrac{7}{3}\)
\(\Rightarrow x=\dfrac{1}{9}\)
Vậy \(x=\dfrac{1}{9}\)
b)\(\dfrac{1}{7}B=\dfrac{1}{10.18}+\dfrac{1}{18.26}+\dfrac{1}{26.34}+...+\dfrac{1}{802.810}\)
\(\dfrac{1}{7}B=\dfrac{1}{8}\left(\dfrac{8}{10.18}+\dfrac{8}{18.26}+\dfrac{8}{26.34}+...+\dfrac{8}{802.810}\right)\)
\(\dfrac{1}{7}B=\dfrac{1}{8}\left(\dfrac{1}{10}-\dfrac{1}{18}+\dfrac{1}{18}-\dfrac{1}{26}+\dfrac{1}{26}-\dfrac{1}{34}+...+\dfrac{1}{802}-\dfrac{1}{810}\right)\)
\(\dfrac{1}{7}B=\dfrac{1}{8}\left(\dfrac{1}{10}-\dfrac{1}{810}\right)\)
\(\dfrac{1}{7}B=\dfrac{1}{8}.\dfrac{8}{81}\)
\(\dfrac{1}{7}B=\dfrac{1.8}{8.81}\)
\(\dfrac{1}{7}B=\dfrac{1}{81}\)
\(B=\dfrac{1}{81}:\dfrac{1}{7}\)
\(B=\dfrac{7}{81}\)
3/ Chu vi hình chữ nhật:
\(\left(\dfrac{1}{4}+\dfrac{3}{10}\right)\cdot2=\dfrac{11}{10}\) (chưa biết đơn vị)
Diện tích hình chữ nhật:
\(\dfrac{1}{4}\cdot\dfrac{3}{10}=\dfrac{11}{20}\) (chưa biết đơn vị)
a) Ta có :
\(x:4\dfrac{1}{3}=-2,5\)
\(x=-2,5\times4\dfrac{1}{3}\)
\(x=-\dfrac{65}{6}\)
b) Ta có :
\(x:\dfrac{-3}{5}=\dfrac{-10}{21}\)
\(x=\dfrac{-10}{21}\times\dfrac{-3}{5}\)
\(x=\dfrac{2}{7}\)
c)\(\dfrac{2}{3}x-\dfrac{1}{2}=\dfrac{1}{10}\)
\(\dfrac{2}{3}x=\dfrac{1}{10}+\dfrac{1}{2}\)
\(\dfrac{2}{3}x=\dfrac{3}{5}\)
\(x=\dfrac{3}{5}:\dfrac{2}{3}\)
\(x=\dfrac{3}{5}\)
d) \(\dfrac{1}{2}x+\dfrac{1}{2}=\dfrac{5}{2}\)
\(\dfrac{1}{2}x=2\)
\(x=2:\dfrac{1}{2}\)
\(x=4\)
~ Chúc bn học tốt ~
a, \(x:4\dfrac{1}{3}=-2,5.\)
\(x:\dfrac{13}{3}=\dfrac{-5}{2}.\)
\(x=\dfrac{-5}{2}.\dfrac{13}{3}.\)
\(x=\dfrac{-65}{6}.\)
b, \(x:\dfrac{-3}{5}=\dfrac{-10}{21}.\)
\(x=\dfrac{-10}{21}.\dfrac{-3}{5}.\)
\(x=\dfrac{30}{105}=\dfrac{2}{7}.\)
c, \(\dfrac{2}{3}x-\dfrac{1}{2}=\dfrac{1}{10}.\)
\(\dfrac{2}{3}x=\dfrac{1}{10}+\dfrac{1}{2}.\)
\(\dfrac{2}{3}x=\dfrac{1}{10}+\dfrac{5}{10}.\)
\(\dfrac{2}{3}x=\dfrac{3}{5}.\)
\(x=\dfrac{3}{5}:\dfrac{2}{3}.\)
\(x=\dfrac{3}{5}.\dfrac{3}{2}.\)
\(x=\dfrac{9}{10}.\)
d, \(\dfrac{1}{2}x+\dfrac{1}{2}=\dfrac{5}{2}.\)
\(\dfrac{1}{2}x=\dfrac{5}{2}-\dfrac{1}{2}.\)
\(\dfrac{1}{2}x=2.\)
\(x=2:\dfrac{1}{2}.\)
\(x=2.2.\)
\(x=4.\)
~ Chúc bn học tốt!!! ~
Bài mik đúng thì nhớ tick mik nha!!!
\(A=\dfrac{1}{1^2}+\dfrac{1}{2^2}+\dfrac{1}{3^2}+...+\dfrac{1}{50^2}\\ \Rightarrow2A=2+\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{50}\\ \Rightarrow2A-A=2-\dfrac{1}{50^2}\\ A=\dfrac{5000}{50^2}-\dfrac{1}{50^2}=\dfrac{5000-1}{50^2}=\dfrac{4999}{2500}\)
Giả sử \(B=\dfrac{173}{100}=\dfrac{4325}{2500}\), mà \(\dfrac{4999}{2500}>\dfrac{4325}{2500}\)
\(\Rightarrow A>B\)
ừ Vy Nguyễn, mik làm nè:
e, \(\dfrac{-2}{3}-\dfrac{1}{3}\left(2x-5\right)=\dfrac{3}{2}.\)
\(\dfrac{1}{3}\left(2x-5\right)=\dfrac{-2}{3}-\dfrac{3}{2}.\)
\(\dfrac{1}{3}\left(2x-5\right)=\dfrac{-4}{6}+\dfrac{-9}{6}.\)
\(\dfrac{1}{3}\left(2x-5\right)=\dfrac{-13}{6}.\)
\(2x-5=\dfrac{-13}{6}:\dfrac{1}{3}.\)
\(2x-5=\dfrac{-13}{6}.3.\)
\(2x-5=\dfrac{-13}{2}.\)
\(2x=\dfrac{-13}{2}+5.\)
\(2x=\dfrac{-13}{2}+\dfrac{10}{2}.\)
\(2x=\dfrac{-3}{2}.\)
\(x=\dfrac{-3}{2}:2.\)
\(x=\dfrac{-3}{2.2}=\dfrac{-3}{4}.\)
g, \(\dfrac{2}{5}x+\dfrac{1}{2}=\dfrac{-3}{4}.\)
\(\dfrac{2}{5}x=\dfrac{-3}{4}-\dfrac{1}{2}.\)
\(\dfrac{2}{5}x=\dfrac{-3}{4}+\dfrac{-2}{4}.\)
\(\dfrac{2}{5}x=\dfrac{-5}{4}.\)
\(x=\dfrac{-5}{4}:\dfrac{2}{5}.\)
\(x=\dfrac{-5}{4}.\dfrac{5}{2}.\)
\(x=\dfrac{-25}{8}.\)
h, \(\left(2x-2\dfrac{4}{5}\right):3\dfrac{1}{8}=1\dfrac{3}{5}.\)
\(\left(2x-2\dfrac{4}{5}\right)=\dfrac{8}{5}.\dfrac{25}{8}.\)
\(\left(2x-2\dfrac{4}{5}\right)=5.\)
\(2x=5+2\dfrac{4}{5}.\)
\(2x=7\dfrac{4}{5}.\)
\(x=7\dfrac{4}{5}:2.\)
\(x=\dfrac{39}{10}.\)
(còn tiếp ở phần sau!!!)
Tiếp:
i, \(3,2x-\left(\dfrac{4}{5}+\dfrac{2}{3}\right):3\dfrac{2}{3}=\dfrac{7}{20}.\)
\(\dfrac{16}{5}x-\left(\dfrac{4}{5}+\dfrac{2}{3}\right)=\dfrac{7}{20}.\dfrac{11}{3}.\)
\(\dfrac{16}{5}x-\left(\dfrac{4}{5}+\dfrac{2}{3}\right)=\dfrac{77}{60}.\)
\(\dfrac{16}{5}x-\left(\dfrac{12}{15}+\dfrac{10}{15}\right)=\dfrac{77}{60}.\)
\(\dfrac{16}{5}x-\dfrac{22}{15}=\dfrac{77}{60}.\)
\(\dfrac{16}{5}x=\dfrac{77}{60}+\dfrac{22}{15}.\)
\(\dfrac{16}{5}x=\dfrac{77}{60}+\dfrac{88}{60}.\)
\(\dfrac{16}{5}x=\dfrac{165}{60}=\dfrac{11}{4}.\)
\(x=\dfrac{11}{4}:\dfrac{16}{5}.\)
\(x=\dfrac{11}{4}.\dfrac{5}{16}=\dfrac{55}{64}.\)
k, \(\left(\dfrac{3x}{7}+1\right):\left(-4\right)=\dfrac{-1}{28}.\)
\(\left(\dfrac{3x}{7}+1\right)=\dfrac{-1}{28}.\left(-4\right).\)
\(\left(\dfrac{3x}{7}+1\right)=\dfrac{1}{7}.\)
\(\dfrac{3x}{7}=\dfrac{1}{7}-1.\)
\(\dfrac{3x}{7}=\dfrac{1}{7}-\dfrac{7}{7}.\)
\(\dfrac{3x}{7}=\dfrac{-6}{7}.\)
\(\Rightarrow3x=-6.\)
\(\Rightarrow x=-6:3=-2.\)
~ Chúc bn học tốt!!! ~
Bài mik đúng thì nhớ tik mik nha!!!
a, \(\dfrac{x+2}{2}=\dfrac{6}{12}\Rightarrow6x+12=6\Leftrightarrow x=-1\)
b, đk : x khác 1
\(\dfrac{8}{x-1}=-\dfrac{16}{22}=-\dfrac{8}{11}\Rightarrow x-1=-11\Leftrightarrow x=-10\)(tm)
thank
