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điên à

a: 2/3=10/15

4/5=12/15

mà 10/15<12/15

nên 2/3<4/5

b: 7/9=7/9

1/3=3/9

mà 7/9>3/9

nên 7/9>1/3

a) \(\dfrac{2}{3}< \dfrac{4}{5}\)

Vì \(\dfrac{10}{15}< \dfrac{12}{15}\)

b) \(\dfrac{7}{9}>\dfrac{1}{3}\) 

Vì \(\dfrac{14}{18}>\dfrac{6}{18}\)

a.<

b.>

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b) >
quy đồng lên là được

Ta có : \(5^7.25^7=5^7.\left(5^2\right)^7=5^7.5^{14}=5^{21}\)

            \(625^6=\left(5^4\right)^6=5^{24}\)

mà 21 < 24

\(\Rightarrow5^{21}< 5^{24}\)

\(\Rightarrow5^7.25^7< 625^6\)

5⁷. 25⁷ và 625⁶

5⁷. 25⁷ = ( 5 . 25 )⁷= 125⁷= 125⁶.125

625⁶ = (125.5)⁶ = 125⁶ . 5 ⁶= 125⁶. 15625

vì 125 < 15625 => 5⁷. 25⁷ < 625⁶

\(1,\\ a,\Leftrightarrow4^{5-x}=4^2\Leftrightarrow5-x=2\Leftrightarrow x=3\\ b,\Leftrightarrow\left[{}\begin{matrix}x-1=5\\x-1=-5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=6\\x=-4\end{matrix}\right.\\ c,\Leftrightarrow2x+1=3\Leftrightarrow x=2\\ 2,\\ a,3^{100}=\left(3^2\right)^{50}=9^{50}\\ b,2^{98}=\left(2^2\right)^{49}=4^{49}< 9^{49}\\ c,5^{30}=5^{29}\cdot5< 6\cdot5^{29}\\ d,3^{30}=\left(3^3\right)^{10}=27^{10}>8^{10}\\ 4,\\ a,\Leftrightarrow5\left(x-10\right)=10\\ \Leftrightarrow x-10=2\Leftrightarrow x=12\\ b,\Leftrightarrow3\left(70-x\right)+5=92\\ \Leftrightarrow3\left(70-x\right)=87\\ \Leftrightarrow70-x=29\\ \Leftrightarrow x=41\\ c,\Leftrightarrow16+x-5=315-230=85\\ \Leftrightarrow x=74\\ d,\Leftrightarrow2^x-5+74=707:\left(16-9\right)=707:7=101\\ \Leftrightarrow2^x=32=2^5\\ \Leftrightarrow x=5\)

bài 4 đâu bạn r =))

a) Ta có: 

\(A=-3\cdot7\cdot\left(-2\right)\cdot\left(-13\right)\)

\(A=-21\cdot26\)

\(A=-546\)

\(B=-1\cdot\left(-2\right)\cdot\left(-3\right)\cdot\left(-4\right)\cdot5\)

\(B=2\cdot12\cdot5\)

\(B=2\cdot60\)

\(B=120\)

Mà: \(120>-546\)

\(\Rightarrow B>A\)

Bài 2: 

a: 5/4<7/4

b: 2/3=34/51

9/17=27/51

mà 34>27

nên 2/3>9/17

Bài 3: 

a: 1/3+3/8=8/24+9/24=17/24

b: 7/6+5/18=21/18+5/18=26/18=13/9

Từng bài 1 thôi nhé

nhóm 3 căp thành 1 nhóm