Bài 1 :

a) \(\frac{12}{21}-\frac{3}{7}+\left(-\frac{2}{3}\right)=\frac{4}{7}-\frac{3}{7}+\left(-\frac{2}{3}\right)=\frac{1}{7}-\frac{2}{3}=-\frac{11}{21}\)

b) \(\left(-\frac{25}{13}\right)+\left(-\frac{9}{17}\right)+\frac{12}{13}+\left(-\frac{25}{17}\right)\)

\(=\left[\left(-\frac{25}{13}\right)+\frac{12}{13}\right]+\left[\left(-\frac{9}{17}\right)+\left(-\frac{25}{17}\right)\right]\)

\(=-1+\left(-2\right)=-1-2=-3\)

c) \(\frac{5}{9}\cdot\frac{7}{13}+\frac{5}{9}\cdot\frac{9}{13}-\frac{5}{9}\cdot\frac{3}{13}=\frac{5}{9}\left(\frac{7}{13}+\frac{9}{13}-\frac{3}{13}\right)=\frac{5}{9}\cdot1=\frac{5}{9}\)

Bài 2 :

a)  \(\frac{2}{3}x+\frac{5}{7}=\frac{3}{10}\)

=> \(\frac{2}{3}x=\frac{3}{10}-\frac{5}{7}=-\frac{29}{70}\)

=> \(x=\left(-\frac{29}{70}\right):\frac{2}{3}=\left(-\frac{29}{70}\right)\cdot\frac{3}{2}=-\frac{87}{140}\)

b) \(x:\frac{5}{2}-\frac{1}{2}=-\frac{2}{3}\)

=> \(x:\frac{5}{2}=-\frac{2}{3}+\frac{1}{2}=-\frac{1}{6}\)

=> \(x=\left(-\frac{1}{16}\right)\cdot\frac{5}{2}=-\frac{5}{32}\)

c) Bạn chỉ cần xét hai trường hợp âm và dương thôi :>

a) 2^3x+2 = 4^x+5 = (2²)^x+5 = 2^2x+10

=> 3x + 2 = 2x + 10

=> 3x - 2x = 10 - 2

x = 8

b) 3^-1.3^x + 9.3^x = 28

3^x. ( 3^-1 + 9) = 28

3^x. 28/3 = 28

3^x = 3 = 3¹

=> x = 1

     \(2^{3x+2}=4^{x+5}\)

\(\Rightarrow2^{3x+2}=\left(2^2\right)^{x+5}\)

\(\Rightarrow3x+2=2\left(x+5\right)\)

\(\Rightarrow3x+2=2x+10\)

\(\Rightarrow3x-2x=10-2\Rightarrow x=8\)

      \(3^{-1}.3^x+9.3^x=28\)

\(\Rightarrow\frac{1}{3}.3^x+9.3^x=28\)

\(\Rightarrow3^x.\left(9+\frac{1}{3}\right)=28\)

\(\Rightarrow3^x.\frac{28}{3}=28\)

\(\Rightarrow3^x=3\Rightarrow x=1\)

Chúc bạn học tốt.

Ta có :

\(\frac{2^9.3^{10}+2^8.3^7.135}{2^{10}.3^{10}+2^9.3^{11}}\)\(=\frac{2^9.3^{10}+2^8.3^7.3^3.5}{2^{10}.3^{10}+2^9.3^{11}}=\frac{2^9.3^{10}+2^8.3^{10}.5}{2^{10}.3^{10}+2^9.3^{11}}=\frac{2^8.3^{10}.\left(2+5\right)}{2^8.3^{10}.\left(2^2+2.3\right)}=\frac{7}{10}\)

Ủng hộ mk nha !!!! ***

\(=\frac{2^9.3^{10}+2^8.3^7.3^3.5}{2^{10}.3^{10}+2^9.3^{11}}=\frac{2^8.3^{10}.\left(2+5\right)}{2^8.3^{10}.\left(2^2+2.3\right)}=\frac{7}{10}\)

15116544

tích mình nhé các bạn thân yêu

lớp 5 chưa học

Tim x€n

a.72.2-6.(2x+5)=10^5:10^3

b.(5x+3^4).6^8=6^9.3^4

9.3^x+1= 81

3^2.3^x+1= 81

3^x+3=81

3^x+3=3^4

Suy ra x+3=4

               x= 4-3

               x=1

\(9.3^{x+1}=81\)

\(\Rightarrow3^{x+1}=81:9\)

\(\Rightarrow3^{x+1}=9\)

\(\Rightarrow3^{x+1}=3^2\)

\(\Rightarrow x+1=2\)

\(\Rightarrow x=1\)

`10+2x=45:9×3`

`10+2x=5×3`

`10+2x=15`

`2x=15-10`

`2x=5`

`x=5/2`

10+2x=45:9.3

=>10+2x=5.3

=>10+2x=15

=>2x=15-10

=>2x=5

=>x=5:2

=>x=2,5

Vậy x=2,5

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