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( 8 x - 12 ) ^ 3 = 125
( 8 x - 12 ) ^ 3 = 5 ^ 3
=> 8 x - 12 = 5
8 x = 17
x = \(\frac{17}{8}\)
-5/9 . 13/28 - 13/28 . 4/9
= 13/28 . (-5/9 - 4/9)
= 13/28 . (-1)
= -13/28
`-5/9 xx 13/28 - 13/28 xx 4/9`
`= 13/28 xx ((-5)/9 - 4/9)`
`= 13/28 xx (-1)`
`= -13/28`
a,
n5 -n=n(n4 -1)=n(n2 +1)(n+1)(n-1)
vi n,n+1,n-1 la 3 so tu nhien lien tiep nen h cau chung chia het cho 3 va 2
mat khac (2;3)=1 nen S= n(n+1)(n-1)(n2 +1)chia het cho 6
xet n=5k
ma(5;6)=1nen Schia het cho 30
tuong tu voi n=5k+1 thi n-1 chia het cho 5
voi n=5k+2 thi n2 +1 chia het cho 5
voi n=5k+3 thi n2 +1 chia het cho 5
voi n=5k+4 thi n+1 chia het cho 5
vay voi moi n nguyen thi n5 -n chia het cho 30
\(A=\frac{13}{28}\left(-\frac{5}{9}-\frac{4}{9}\right)=\frac{13}{28}\left(-\frac{9}{9}\right)=\frac{13}{28}\left(-1\right)\)
=> \(A=-\frac{13}{28}\)
A= -5/9x 13/28- 13/28x 4/9
=13/28x (-5/9- 4/9)
=13/28x (-1)
=-13/28
Bài làm
a) \(\left(\frac{3}{8}+\frac{-1}{4}+\frac{5}{12}\right):\frac{2}{3}\)
\(=\left(\frac{9}{24}+\frac{-6}{24}+\frac{10}{24}\right).\frac{3}{2}\)
\(=\frac{13}{24}.\frac{3}{2}\)
\(=\frac{39}{48}\)
b) \(\frac{-5}{7}.\frac{2}{11}+\frac{-5}{7}.\frac{9}{11}+1\frac{5}{7}\)
\(=-\frac{5}{7}.\left(\frac{2}{11}+\frac{9}{11}\right)+\frac{12}{7}\)
\(=-\frac{5}{7}.1+\frac{12}{7}\)
\(=\frac{7}{7}\)
\(=1\)
c) \(0,25:\left(10,3-9,8\right)-\frac{3}{4}\)
\(=\frac{25}{100}:\left(0,5\right)-\frac{3}{4}\)
\(=\frac{5}{4}:\frac{1}{2}-\frac{3}{4}\)
\(=\frac{5}{4}.2-\frac{3}{4}\)
\(=\frac{5}{2}-\frac{3}{4}\)
\(=\frac{10}{4}-\frac{3}{4}=\frac{7}{4}\)
d) \(-\frac{5}{9}.\frac{13}{28}-\frac{13}{28}.\frac{4}{9}\)
\(=-\frac{13}{28}\left(\frac{5}{9}+\frac{4}{9}\right)\)
\(=-\frac{13}{28}.\frac{9}{9}\)
\(=-\frac{13}{28}.1\)
\(=-\frac{13}{28}\)
\(\frac{-5}{9}.\frac{13}{28}-\frac{13}{28}.\frac{4}{9}\)
\(=\frac{13}{28}.\left(\frac{-5}{9}-\frac{4}{9}\right)\)
\(=\frac{13}{28}.\left(-1\right)\)
\(=\frac{-13}{28}\)
=13/28.(-5/9-4/9)
=13/28.(-1)
=-13/28