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Đặt \(A=\frac{5^{28}+5^{24}+.........+5^4+1}{5^{30}+5^{28}+5^{26}+.....+5^2+1}=\frac{B}{C}\)

Xét tử \(B=5^{28}+5^{24}+........+5^4+1\)

\(\Rightarrow5^4.B=5^{32}+5^{28}+........+5^8+5^4\)

\(\Rightarrow625.B=5^{32}+5^{28}+........+5^8+5^4\)

\(\Rightarrow625.B-B=624.B=5^{32}-1\)

\(\Rightarrow B=\frac{5^{32}-1}{624}\)

Xét mẫu \(C=5^{30}+5^{28}+5^{26}+........+5^2+1\)

\(\Rightarrow5^2.C=5^{32}+5^{30}+5^{28}+.........+5^4+5^2\)

\(\Rightarrow25.C=5^{32}+5^{30}+5^{28}+........+5^4+5^2\)

\(\Rightarrow25.C-C=24.C=5^{32}-1\)

\(\Rightarrow C=\frac{5^{32}-1}{24}\)

\(\Rightarrow A=\frac{B}{C}=\frac{5^{32}-1}{624}:\frac{5^{32}-1}{24}=\frac{5^{32}-1}{624}.\frac{24}{5^{32}-1}=\frac{24}{624}=\frac{1}{26}\)

a, 128 - 28.(4 - 12)

= 128 - 28.(-8)

= -8 . (-16) - 28 . (-8)

= -8 . (-16 - 28)

= -8 . (-44)

= 352

b, (-28) .32 + 58.(-28) + (-28) . 10

= -28 . (32 + 58 + 10)

= -28 . 100

= -2800

c, (-5 - 7) : (-7 + 5)

= -12 : (-2)

= 6

280 nho like cho minh nhe

Ta có:56x2+28x5 +28

=28x2x2+28x5+28

=28x4+28x5+28

=28x(4+5+1)

=28x10=280

56 x 2 + 28 x 5 + 28
       = 28 x 2 x 2 + 28 x 5 + 28 x 1
       = 28 x 4 + 28 x 5 + 28 x 1
       = 28 x ( 4 + 5 + 1 )
       = 28 x 10
       = 280

kết quả là 3

\(=\)\(\frac{-3}{5}\)\(+\frac{28.43}{5.28.2}\)\(+\frac{4.7.5}{5.4.6}\)\(+\frac{28.21}{5.21.3}\)

\(=\)\(\frac{-3}{5}\)\(+\frac{43}{10}+\frac{7}{6}+\frac{28}{15}\)

\(=\)\(\frac{-48}{90}+\frac{387}{90}+\frac{85}{90}+\frac{168}{90}\)

\(=\)\(\frac{592}{90}\)

\(=\)\(\frac{296}{45}\)

=28+32-28-32+5

=(28-28)+(32-32)+5

=5

28 - ( -32 ) + ( -28 ) - 32 + 5

= 28 + 32 + ( -28 ) - 32 + 5

= ( -28 + 28 ) + ( -32 + 32 ) + 5

= 0 + 0 + 5

= 5 

`2/5 + 9/15= 2/5 + 3/5=5/5=1`

`15/45 + 25/30= 1/3 + 5/6= 2/6+5/6=7/6`

`28/32 + 45/72=7/8+ 5/8=12/8=3/2`

`8/28 + 5/30= 2/7 + 1/6= 12/42 + 7/42= 19/42`

32 + 28 =60

32+28n=60

56 - 5- 9 =42

= 60 +60 -42

=120 -42

=98

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