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\(\frac{1}{3}\) + \(\frac{5}{6}\): \(\left(x-2\frac{1}{5}\right)\)= \(\frac{3}{4}\)
<=> \(\frac{5}{6}\):\(\left(x-2\frac{1}{5}\right)\)= \(\frac{3}{4}\)- \(\frac{1}{3}\)
<=> \(\frac{5}{6}\) : \(\left(x-2\frac{1}{5}\right)\) = \(\frac{5}{12}\)
<=> \(\left(x-2\frac{1}{5}\right)\) = \(\frac{5}{6}\) : \(\frac{5}{12}\)
,<=> \(\left(x-2\frac{1}{5}\right)\)= 2
<=. x = 2 + \(\frac{11}{5}\)
<=> x = \(\frac{21}{5}\)
Gọi biểu thức trên là \(A\). Ta có :
\(A=\frac{1}{4}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)
\(A=\frac{1}{4}+\frac{1}{2}-\frac{1}{6}\)
\(A=\frac{3}{4}-\frac{1}{6}\)
\(A=\frac{7}{12}.\)
Đáp số : \(\frac{7}{12}.\)
\(x-2\frac{1}{4}=3\frac{1}{2}\)
\(x-\frac{9}{4}=\frac{7}{2}\)
\(x=\frac{7}{2}+\frac{9}{4}\)
\(x=\frac{14}{4}+\frac{9}{4}\)
\(x=\frac{23}{4}\)
1) \(1+\frac{1}{3}+1\frac{91}{27}+\frac{1}{81}\)
\(=1+\frac{1}{3}+4+\frac{10}{27}+\frac{1}{81}\)
\(=\left(1+4\right)+\left(\frac{1}{3}+\frac{10}{27}+\frac{1}{81}\right)\)
\(=5+\frac{58}{81}=5\frac{58}{81}\)
2) \(\frac{1}{78}+\frac{1}{91}+\frac{1}{105}+\frac{1}{120}+\frac{1}{136}\)
\(=\frac{1}{6\times13}+\frac{1}{13\times7}+\frac{1}{7\times15}+\frac{1}{15\times8}+\frac{1}{8\times17}\)
\(=\frac{1}{6}-\frac{1}{13}+\frac{1}{13}-\frac{1}{7}+\frac{1}{7}-\frac{1}{15}+\frac{1}{15}-\frac{1}{8}+\frac{1}{8}-\frac{1}{17}\)
(gạch bỏ các số giống nhau)
\(=\frac{1}{6}-\frac{1}{17}=\frac{11}{102}\)
3) \(\frac{1}{6}+\frac{1}{30}+\frac{1}{70}+\frac{1}{126}\)
\(=\frac{1}{2\times3}+\frac{1}{3\times10}+\frac{1}{10\times7}+\frac{1}{7\times18}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{10}+\frac{1}{10}-\frac{1}{7}+\frac{1}{7}-\frac{1}{18}\)
\(=\frac{1}{2}-\frac{1}{18}=\frac{4}{9}\)
chúc bn học tốt!!
công chúa ôri ơi mk viết nhầm đề bài 1
đề bài là 1+1/3+1/9+1/27+1/81
bạn trả lời giúp mk với mk cần gấp lắm
cảm ơn
1)
25 x 7 + 3 x (50-25) x (60 - 60)
=175 +3 x 25 x 0
=175
2)
\(\frac{1}{2}.\frac{3}{4}.\frac{4}{5}.\frac{1}{3}\\ =\frac{1.3.4.1}{2.4.5.3}\\ =\frac{3.4}{3.4.2.5}\\ =\frac{1}{2.5}\\ =\frac{1}{10}\)
\(\frac{1}{4}=0,25;\frac{3}{5}=0,6;\frac{7}{8}=0,875;\frac{3}{2}=1,5\)
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1. 1/2-(x-1/4)=1/3
=> x-1/4=1/2-1/3
=> x-1/4= 1/6
=> x= 1/6+1/4=5/12
2. 3/2*(x-1/2-1)=5/4
=> x-1/2-1=5/4:3/2
=> x-1/2= 5/6+1
=> x = 11/6+1/2
=> x= 7/3
3. 11/2-9/2*(x-3/4)=1
=> 9/2*(x-3/4)= 11/2-1
=> x-3/4 = 9/2:9/2
=> x= 1+3/4
=> x= 7/4
Chúc bạn Hk tốt!!!!!
1. x=\(\frac{5}{12}\)
2. x=\(\frac{7}{3}\)
3. x= \(\frac{7}{4}\)
Chúc bạn Hk tốt!!!
1.\(\frac{4}{3.7}+\frac{4}{7.11}+\frac{4}{11.15}+\frac{4}{15.19}+\frac{4}{19.23}+\frac{4}{23.27}\)
\(=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{4}{23}-\frac{4}{27}\)
\(=\frac{1}{3}-\frac{1}{27}=\frac{9}{27}-\frac{1}{27}=\frac{8}{27}\)
2. Đặt \(A=\frac{3}{14}+\frac{3}{84}+\frac{3}{204}+\frac{3}{374}+\frac{3}{594}+\frac{3}{864}\)
\(\Rightarrow A=\frac{3}{2.7}+\frac{3}{7.12}+...+\frac{3}{27.32}\)
\(\Rightarrow5A=3.\left(\frac{5}{2.7}+\frac{5}{7.12}+...+\frac{5}{27.32}\right)\)
\(\Rightarrow5A=3.\left(\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+...+\frac{1}{27}-\frac{1}{32}\right)\)
\(\Rightarrow5A=3.\left(\frac{1}{2}-\frac{1}{32}\right)\)
\(\Rightarrow5A=3.\frac{15}{32}=\frac{45}{32}\Rightarrow A=\frac{45}{32}:5=\frac{9}{32}\)
3. Đặt \(S=\frac{1}{10}+\frac{1}{40}+\frac{1}{88}+...+\frac{1}{340}\)
\(\Rightarrow3S=\frac{3}{10}+\frac{3}{40}+...+\frac{3}{340}\)
\(\Rightarrow3S=\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{17.20}\)
\(\Rightarrow3S=\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{17}-\frac{1}{20}\)
\(\Rightarrow3S=\frac{1}{2}-\frac{1}{20}=\frac{9}{20}\Rightarrow S=\frac{9}{20}:3=\frac{3}{20}\)
Câu 1:
\(\frac{4}{3.7}+\frac{4}{7.11}+\frac{4}{11.15}+\frac{4}{15.19}+\frac{4}{19.23}+\frac{4}{23.27}\)
\(\Rightarrow\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{15}+\frac{1}{15}-\frac{1}{19}+\frac{1}{19}-\frac{1}{23}+\frac{1}{23}-\frac{1}{27}\)
\(\Rightarrow\frac{1}{3}-\frac{1}{27}\)
\(=\frac{8}{27}\)
\(\frac{1}{2}\div\frac{3}{4}+\frac{1}{6}\div\frac{3}{4}\)
\(=\frac{3}{4}\div\left(\frac{1}{2}+\frac{1}{6}\right)\)
\(=\frac{3}{4}\div\frac{2}{3}\)
\(=\frac{9}{8}\)
\(\frac{1}{2}\div\frac{3}{4}-\frac{1}{6}\div\frac{3}{4}\)
\(=\left(\frac{1}{2}-\frac{1}{6}\right)\div\frac{3}{4}\)
\(=\frac{1}{3}\div\frac{3}{4}\)\
\(=\frac{4}{9}\)
1/2 : 3/4 + 1/6 : 3/4 = 1/2 x 4/3 + 1/6 x 4/3 = 4/3 x (1/2 + 1/6) = 4/3 x 2/3 = 8/9
1/2 : 3/4 - 1/6 : 3/4 = 1/2 x 4/3 - 1/6 x 4/3 = 4/3 x (1/2 - 1/6) = 4/3 x 1/3 = 4/9