Tính:
A=( 1/2 - 1/3 ).( 1/2 - 1/5 ).( 1/2 - 1/7 )...( 1/2 - 1/99 )
K
Khách
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0
16 tháng 7 2021
a) bằng 9 nha bạn
b) thì mik ko bik làm.
Đúng thì bạn tim giúp mik nha bạn. Thx bạn
JK
15 tháng 2 2022
a. \(\dfrac{5}{17}+\dfrac{-5}{34}.\dfrac{2}{5}\)
= \(\dfrac{5}{17}+\dfrac{1}{-17}\)
= \(\dfrac{5}{17}+\dfrac{-1}{17}\)
= \(\dfrac{4}{17}\)
b. \(\dfrac{1}{2}.\dfrac{5}{6}+\dfrac{2}{3}.\dfrac{3}{4}\)
= \(\dfrac{5}{12}+\dfrac{1}{2}\)
= \(\dfrac{5}{12}+\dfrac{6}{12}\)
= \(\dfrac{11}{12}\)
c. \(\left(\dfrac{-2}{5}+\dfrac{1}{3}\right).\left(\dfrac{3}{2}-\dfrac{3}{7}\right)\)
= \(\left(\dfrac{-6}{15}+\dfrac{5}{15}\right).\left(\dfrac{21}{14}-\dfrac{6}{14}\right)\)
= \(\dfrac{-1}{15}.\dfrac{15}{14}\)
= \(\dfrac{-1}{14}\)
d. \(\left(1+\dfrac{1}{2}\right).\left(1+\dfrac{1}{3}\right).\left(1+\dfrac{1}{4}\right)\)
= \(\left(\dfrac{2}{2}+\dfrac{1}{2}\right).\left(\dfrac{3}{3}+\dfrac{1}{3}\right).\left(\dfrac{4}{4}+\dfrac{1}{4}\right)\)
= \(\dfrac{3}{2}.\dfrac{4}{3}.\dfrac{5}{4}\)
= \(\dfrac{5}{2}\)
15 tháng 2 2022
a: \(=\dfrac{5}{34}\cdot\dfrac{2}{5}=\dfrac{2}{34}=\dfrac{1}{17}\)
b: \(=\dfrac{5}{12}+\dfrac{6}{12}=\dfrac{11}{12}\)
c: \(=\dfrac{-6+5}{15}\cdot\dfrac{21-6}{15}=-\dfrac{1}{15}\)
3 tháng 1 2017
\(\text{A = 1-2-3-4+5-6-7-8+9-10-11-12+...........+97-98-99-100}\)
\(\text{A =(1-2-3-4)+(5-6-7-8)+(9-10-11-12)+.............+(97-98-99-100)}\)
\(\text{A =-8+(-16)+(-24)+..................+(-200)}\)
\(\text{A =-8.(1+2+3+......+25)}\)
\(\text{A =-8.[(25-1):1+1.26:2]}\)
\(\text{A =-8.325}\)
\(\text{A =-2600 Vậy A = -2600 }\)
3 tháng 1 2017
=1+(2-3-4+5)+(6-7-8+9)+...+(98-99-100+101)+102
=1+0+0+0+....+102
=103
k mk nha
18 tháng 1
a: \(\dfrac{16}{15}\cdot\dfrac{-5}{14}\cdot\dfrac{54}{24}\cdot\dfrac{56}{21}\)
\(=\dfrac{16}{24}\cdot\dfrac{-5}{15}\cdot\dfrac{54}{21}\cdot\dfrac{56}{14}\)
\(=\dfrac{2}{3}\cdot\dfrac{-1}{3}\cdot\dfrac{18}{7}\cdot4\)
\(=\dfrac{-2\cdot2\cdot4}{7}=-\dfrac{16}{7}\)
b: \(\dfrac{7}{3}\cdot\dfrac{-5}{2}\cdot\dfrac{15}{21}\cdot\dfrac{4}{-5}\)
\(=\dfrac{7}{3}\cdot\dfrac{5}{7}\cdot\dfrac{5}{2}\cdot\dfrac{4}{5}\)
\(=\dfrac{5}{3}\cdot\dfrac{4}{2}=\dfrac{5}{3}\cdot2=\dfrac{10}{3}\)
c: \(\left(-\dfrac{2}{5}+\dfrac{1}{3}\right)\left(\dfrac{3}{2}-\dfrac{3}{7}\right)\)
\(=\dfrac{-2\cdot5+3}{15}\cdot\dfrac{3\cdot7-3\cdot2}{14}\)
\(=\dfrac{-7}{15}\cdot\dfrac{15}{14}=\dfrac{-7}{14}=-\dfrac{1}{2}\)
d: \(\left(\dfrac{1}{2}-\dfrac{1}{3}\right)\left(5-\dfrac{1}{4}\right)\)
\(=\dfrac{3-2}{6}\cdot\dfrac{20-1}{4}\)
\(=\dfrac{1}{6}\cdot\dfrac{19}{4}=\dfrac{19}{24}\)
e: \(\left(\dfrac{4}{5}\right)^2=\dfrac{4^2}{5^2}=\dfrac{16}{25}\)
14 tháng 9 2023
a: \(=\dfrac{13}{3}+\dfrac{17}{6}=\dfrac{26}{6}+\dfrac{17}{6}=\dfrac{43}{6}\)
b: \(=7-\dfrac{8}{3}=\dfrac{21-8}{3}=\dfrac{13}{3}\)
c: \(=\dfrac{17}{7}\cdot\dfrac{7}{4}=\dfrac{17}{4}\)
d: \(=\dfrac{16}{3}:\dfrac{16}{5}=\dfrac{16}{3}\cdot\dfrac{5}{16}=\dfrac{5}{3}\)
