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Ngô Hải Nam ơi bn trả lời giúp mik ik
bài đó là bài 4^* tìm các số nguyên x để mỗi phân số sau đây là số nguyên
Ta có: \(M=\dfrac{9}{40}-\dfrac{11}{60}+\dfrac{13}{84}-\dfrac{15}{112}\)
\(=\dfrac{378}{1680}-\dfrac{308}{1680}+\dfrac{260}{1680}-\dfrac{225}{1680}\)
\(=\dfrac{105}{1680}=\dfrac{1}{16}\)
A bn lướt xuống dưới mà xem cách làm
nhưng của bn là cho 3 ra ngoài nha
\(M=\dfrac{9}{40}-\dfrac{11}{60}+\dfrac{13}{84}-\dfrac{15}{112}\)
\(M=\left(\dfrac{90}{40}-\dfrac{11}{60}\right)+\left(\dfrac{13}{84}-\dfrac{15}{112}\right)\)
\(M=\dfrac{27}{120}-\dfrac{22}{120}+\dfrac{52}{336}-\dfrac{45}{336}\)
\(M=\dfrac{5}{120}+\dfrac{7}{336}\)
\(M=\dfrac{1}{24}+\dfrac{1}{48}\)
\(M=\dfrac{3}{48}=\dfrac{1}{16}\)
M=\(\dfrac{9}{40}-\dfrac{11}{60}+\dfrac{13}{84}-\dfrac{15}{112}\)
M=\(\dfrac{1}{24}+\dfrac{13}{84}-\dfrac{15}{112}\)
M=\(\dfrac{11}{56}-\dfrac{15}{112}\)
M=\(\dfrac{1}{16}\)
ạ
Giải:
(1-1/22).(1-1/32).(1-1/42).....(1-1/102)
=3/2.2 . 8/3.3 . 15/4.4 . ... . 99/10.10
=1.3.2.4.3.5.....9.11/2.2.3.3.4.4.....10.10
=1.2.3.....9/2.3.4.....10 . 3.4.5....11/2.3.4.....10
=1/10.11/2
=11/20
Chúc bạn học tốt!
S sẽ có 30 số hạng. Nhóm thành 3 nhóm, mỗi nhóm 101 số hạng.
S= (1/31+1/32+...+1/40) + (1/41 + 1/42 +...+1/50) + (1/51 +1/52+...+1/60)
S < (1/30 + 1/30 +...+ 1/30) + ( 1/40 +1/40+...+1/40) + (1/50 +1/50+...+1/50)
S < 1/30 + 1/40 +1/50 ; S < 47/60 < 48/60 = 4/5 (1)
S > (1/40 + 1/40 +...=1/40) + (1/50 + 1/50 +...+1/50) + (1/60 +1/60+...+1/60)
S < 10/40 + 10/50 +10/60 ; S > 37/60 > 36/60 = 3/5 (2)
Tư (1) và (2) => 3/5 < S < 4/5
NHỚ TICK CHO MINK NHA, CHÚC BẠN HỌC TỐT
S=(\(\dfrac{1}{31}\)+\(\dfrac{1}{32}\)+...+\(\dfrac{1}{40}\))+(\(\dfrac{1}{41}\)+\(\dfrac{1}{42}\)+...+\(\dfrac{1}{50}\))+(\(\dfrac{1}{51}\)+\(\dfrac{1}{52}\)+...+\(\dfrac{1}{60}\))
=>\(\dfrac{10}{40}\)+\(\dfrac{10}{50}\)+\(\dfrac{10}{60}\)< S < \(\dfrac{10}{30}\)+\(\dfrac{10}{40}\)+\(\dfrac{10}{50}\)
=>\(\dfrac{37}{60}\)< S <\(\dfrac{47}{60}\)
=>\(\dfrac{3}{5}\)=\(\dfrac{36}{60}\)<\(\dfrac{37}{60}\)< S < \(\dfrac{47}{60}\)<\(\dfrac{48}{60}\)=\(\dfrac{4}{5}\)
=> \(\dfrac{3}{5}\)< S <\(\dfrac{4}{5}\)
`(x+2)/3=(x-4)/5`
`<=> (x+2)*5=3(x-4)`
`<=> 5x+10=3x-12`
`<=> 5x-3x=-12-10`
`<=> 2x=-22`
`<=> x=-11`
ctv olm có mặt ạ
A = \(\dfrac{3}{24}\) + \(\dfrac{3}{40}\) + \(\dfrac{3}{60}\) + \(\dfrac{3}{84}\) + \(\dfrac{3}{112}\)
A = 3. ( \(\dfrac{2}{2.24}\) + \(\dfrac{2}{2.40}\) + \(\dfrac{2}{2.60}\)+ \(\dfrac{2}{2.84}\) + \(\dfrac{2}{2.112}\))
A = 3 .( \(\dfrac{2}{48}\) + \(\dfrac{2}{80}\) + \(\dfrac{2}{120}\) + \(\dfrac{2}{168}\) + \(\dfrac{2}{224}\))
A = 3. ( \(\dfrac{2}{6.8}\) + \(\dfrac{2}{8.10}\) + \(\dfrac{2}{10.12}\) + \(\dfrac{2}{12.14}\)+ \(\dfrac{2}{14.16}\))
A = 3.( \(\dfrac{1}{6}\) - \(\dfrac{1}{8}\) + \(\dfrac{1}{8}\) - \(\dfrac{1}{10}\) + \(\dfrac{1}{10}\)- \(\dfrac{1}{12}\) + \(\dfrac{1}{12}\) - \(\dfrac{1}{14}\) + \(\dfrac{1}{14}\) - \(\dfrac{1}{16}\))
A = 3.(\(\dfrac{1}{6}\) - \(\dfrac{1}{16}\))
A = 3. \(\dfrac{5}{48}\)
A = \(\dfrac{15}{48}\)
A = \(\dfrac{5}{16}\)