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Những câu hỏi liên quan
DT
0
TK
1
N
1
17 tháng 2 2023
Ta quy về dạng tổng quát xét cho dễ nhé.
\(\dfrac{1}{x\cdot\left(x+2\right)}=\dfrac{1}{2}.\dfrac{2}{x.\left(x+2\right)}=\dfrac{1}{2}.\left(\dfrac{1}{x}-\dfrac{1}{x-2}\right)\)
Từ đó áp dụng dạng tổng quát để rút gọn là ra.
Chúc em học tốt!
NL
Nguyễn Lê Phước Thịnh
CTVHS
20 tháng 12 2021
e: \(=\dfrac{1}{6}-\dfrac{4}{9}+\dfrac{5}{18}=\dfrac{3-8+5}{18}=0\)
HT
1
21 tháng 8 2023
\(\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{20}}{\dfrac{19}{1}+\dfrac{18}{2}+\dfrac{17}{3}+....+\dfrac{1}{19}}\)
\(=\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{20}}{1+\left(\dfrac{18}{2}+1\right)+\left(\dfrac{17}{3}+1\right)+\left(\dfrac{1}{19}+1\right)}\)
\(=\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{20}}{1+\dfrac{20}{2}+\dfrac{20}{3}+...+\dfrac{20}{19}}\)
\(=\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{20}}{20.\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{19}+\dfrac{1}{20}\right)}\)
\(=\dfrac{1}{20}\)
MN
1
6 tháng 5 2021
bạn viết vậy khó hiểu quá bạn viết bằng kí tự phân số ik ạ
NL
Nguyễn Lê Phước Thịnh
CTVHS
14 tháng 11 2025
Bài 1:
\(\frac14+\frac23=\frac{3}{12}+\frac{8}{12}=\frac{3+8}{12}=\frac{11}{12}\)
\(\frac27+\frac23=\frac{6}{21}+\frac{14}{21}=\frac{6+14}{21}=\frac{20}{21}\)
\(\frac25+\frac13=\frac{6}{15}+\frac{5}{15}=\frac{6+5}{15}=\frac{11}{15}\)
\(\frac23+\frac12=\frac46+\frac36=\frac{4+3}{6}=\frac76\)
\(\frac13+\frac35=\frac{5}{15}+\frac{9}{15}=\frac{5+9}{15}=\frac{14}{15}\)
\(\frac45+\frac13=\frac{12}{15}+\frac{5}{15}=\frac{12+5}{15}=\frac{17}{15}\)
\(\frac18+\frac34=\frac18+\frac68=\frac{1+6}{8}=\frac78\)
\(\frac{1}{36}+\frac{5}{12}=\frac{1}{36}+\frac{15}{36}=\frac{1+15}{36}=\frac{16}{36}=\frac49\)
\(\frac13+\frac16+\frac{1}{18}=\frac{6}{18}+\frac{3}{18}+\frac{1}{18}=\frac{6+3+1}{18}=\frac{10}{18}=\frac59\)
Bài 2:
\(\frac{15}{16}-\frac{3}{16}=\frac{15-3}{16}=\frac{12}{16}=\frac34\)
\(\frac{17}{18}-\frac56=\frac{17}{18}-\frac{15}{18}=\frac{17-15}{18}=\frac{2}{18}=\frac19\)
\(\frac34-\frac49=\frac{27}{36}-\frac{16}{36}=\frac{27-16}{36}=\frac{11}{36}\)
\(\frac12-\frac25=\frac{5}{10}-\frac{4}{10}=\frac{5-4}{10}=\frac{1}{10}\)
\(\frac56-\frac{3}{10}=\frac{25}{30}-\frac{9}{30}=\frac{25-9}{30}=\frac{16}{30}=\frac{8}{15}\)
\(3-\frac13=\frac93-\frac13=\frac{9-1}{3}=\frac83\)
\(\frac45-\frac{1}{10}=\frac{8}{10}-\frac{1}{10}=\frac{7}{10}\)
\(\frac52-1=\frac{5-2}{2}=\frac32\)
\(\frac58-\frac25=\frac{25}{40}-\frac{16}{40}=\frac{25-16}{40}=\frac{9}{40}\)
HT
0
30 tháng 1 2023
\(A=\dfrac{19+\dfrac{18}{2}+\dfrac{17}{3}+\dfrac{16}{4}+...+\dfrac{1}{19}}{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{20}}\)
Biến đổi tử số
\(19+\dfrac{18}{2}+\dfrac{17}{3}+\dfrac{16}{4}+...+\dfrac{1}{19}\)
= 1 + \(\left(1+\dfrac{18}{2}\right)+\left(1+\dfrac{17}{3}\right)+\left(1+\dfrac{16}{4}\right)+...+\left(1+\dfrac{1}{19}\right)\)
= \(\dfrac{20}{20}+\dfrac{20}{2}+\dfrac{20}{3}+...+\dfrac{1}{19}\)
= 20 x \(\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{19}+\dfrac{1}{20}\right)\)
Vậy \(A=\dfrac{19+\dfrac{18}{2}+\dfrac{17}{3}+\dfrac{16}{4}+...+\dfrac{1}{19}}{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{20}}\)
= \(\dfrac{20\times\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{19}+\dfrac{1}{20}\right)}{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{20}}=20\)
Vậy A = 20
\(8^{15}\times4^{13}=2^{45}\times2^{26}=2^{71}\)
\(\left(\frac{1}{2}\right)^{18}\times\left(\frac{1}{4}\right)^{24}=\left(\frac{1}{2}\right)^{18}\times\left(\frac{1}{2}\right)^{48}=\left(\frac{1}{2}\right)^{66}\)
\(9^{12}\times27^{10}=3^{24}\times3^{30}=3^{54}\)
\(8^{15}\cdot4^{13}=\left(4^2\right)^{15}\cdot4^{13}=4^{30}\cdot4^{13}=4^{43}\)
\(\left(\frac{1}{2}\right)^{18}\cdot\left(\frac{1}{4}\right)^{24}=\left(\frac{1}{2}\right)^{18}\cdot\left[\left(\frac{1}{2}\right)^2\right]^{24}=\left(\frac{1}{2}\right)^{66}\)
\(9^{12}\cdot27^{10}=3^{36}\cdot3^{30}=3^{66}\)