Câu 1 : 

a, \(\frac{3\left(2x+1\right)}{4}-\frac{5x+3}{6}=\frac{2x-1}{3}-\frac{3-x}{4}\)

\(\Leftrightarrow\frac{6x+3}{4}+\frac{3-x}{4}=\frac{2x-1}{3}+\frac{5x+3}{6}\)

\(\Leftrightarrow\frac{5x+6}{4}=\frac{9x+1}{6}\Leftrightarrow\frac{30x+36}{24}=\frac{36x+4}{24}\)

Khử mẫu : \(30x+36=36x+4\Leftrightarrow-6x=-32\Leftrightarrow x=\frac{32}{6}=\frac{16}{3}\)

tương tự 

\(\frac{19}{4}-\frac{2\left(3x-5\right)}{5}=\frac{3-2x}{10}-\frac{3x-1}{4}\)

\(< =>\frac{19.5}{20}-\frac{8\left(3x-5\right)}{20}=\frac{2\left(3-2x\right)}{20}-\frac{5\left(3x-1\right)}{20}\)

\(< =>95-24x+40=6-4x-15x+5\)

\(< =>-24x+135=-19x+11\)

\(< =>5x=135-11=124\)

\(< =>x=\frac{124}{5}\)

\(\left(1-\frac{3}{10}-x\right):\left(\frac{19}{10}-1-\frac{2}{5}\right)+\frac{4}{5}=1\)

\(\Rightarrow\left(\frac{7}{10}-x\right):\frac{1}{2}=\frac{1}{5}\\ \frac{7}{10}-x=\frac{1}{5}.\frac{1}{2}\\ \frac{7}{10}-x=\frac{1}{10}\\ \Rightarrow x=\frac{7}{10}-\frac{1}{10}=\frac{3}{5}\)

/ là chia à

\(\left(1-\frac{3}{10}-x\right):\left(\frac{19}{10}-1-\frac{2}{5}\right)+\frac{4}{5}=1\)

\(\Rightarrow\left(\frac{7}{10}-x\right):\frac{1}{2}+\frac{4}{5}=1\)

\(\Rightarrow\left(\frac{7}{10}-x\right):\frac{1}{2}=\frac{1}{5}\)

\(\Rightarrow\frac{7}{10}-x=\frac{1}{10}\)

\(\Rightarrow x=\frac{3}{5}\)

3 x 15 + 21 x 15 + 85 x 5

= 45 + 315 + 425

= 785

15 - 30 + 40 

= 25

21 + 19 - 50 + 10

= 0

\(\dfrac{1}{5}-\dfrac{1}{4}+2\)

\(=-\dfrac{1}{20}+2\)

\(=\dfrac{39}{20}\)

\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)

\(=\dfrac{5}{12}\times\dfrac{1}{4}\)

\(=\dfrac{5}{12}\times\dfrac{3}{12}\)

\(=\dfrac{5}{48}\)

\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)

\(=-\dfrac{9}{20}\)

\(3\times15+21\times15+85\times5\\ =15\times\left(3+21\right)+425\\ =15\times24+425\\ =360+425\\ =785\)

\(15-30+40\\ =\left(15+40\right)-30\\ =55-30\\ =25\)

\(21+19-50+10\\ =\left(21+19\right)-\left(50-10\right)\\ =40-40\\ =0\)

\(\dfrac{1}{5}-\dfrac{1}{4}+2\)

\(=\dfrac{4}{20}-\dfrac{5}{20}+\dfrac{40}{20}\)

\(=\dfrac{\left(4+40\right)}{20}-\dfrac{5}{20}\)

\(=\dfrac{44}{20}-\dfrac{5}{20}\)

\(=\dfrac{39}{20}\)

\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)

\(=\dfrac{5}{12}\times\dfrac{1}{4}\)

\(=\dfrac{5}{48}\)

\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)

\(=\dfrac{2}{20}+\dfrac{4}{20}-\dfrac{15}{20}\)

\(=\dfrac{6}{20}-\dfrac{15}{20}\)

\(=-\dfrac{9}{20}\)

\(1\dfrac{1}{6}+1\dfrac{1}{4}=\dfrac{7}{6}+\dfrac{5}{4}=\dfrac{14}{12}+\dfrac{15}{12}=\dfrac{14+15}{12}=\dfrac{19}{12}=1\dfrac{7}{12}\)\(2\dfrac{2}{3}\div1\dfrac{3}{19}=\dfrac{8}{3}\div\dfrac{22}{19}=\dfrac{8}{3}\times\dfrac{19}{22}=\dfrac{8\times19}{3\times22}=\dfrac{76}{33}\)

tìm x:

a)x=5/8-1/4
   x=5/8-2/8
   x=3/8
b)x=1/10+3/5
   x=1/10+3/10
   x=4//10
c)  x = 7/8 - 1/4

       x = 5/8

d)x=1/4x3/2
    x=3/8

đ) X = 6/11 : 2/7

     X =6/11x7/2

     X= 21/11

e)X=4/5:2/3

     X=4/5x3/2

     X=12/10=6/5

tính

a) 7/9 x 5/6=35/54

b) 1/5 : 7/10=1/5x10/7

                   =10/35=2/7

c) 6/5 x ( 2/3 - 3/5 )=6/5x(9/15-10/15)

                              =6/5x3/5

                              =18/25

d) 1/4 : 3/8 x 6/5=1/4x8/3x6/5

                           =2/3x6/5

                           =12/15=4/5

không biết có đúng không nhưng đúng nhớ tick cho mình nha,mình cảm ơnn

a) =>  (35:x+3)*15 = 165-15=150

=> 35:x+3 = 150:15=10

=> 35:x = 10-3 = 7

=> x = 35:7 = 5

b) => 1*3/10x :1/2 +4/5 =1

=> 1*3/10x:1/2 =1-4/5=1/5

=> 1*3/10x = 1/5 *1/2 =1/10

=> 3/10-x = 1/10

=> x = 3/10 - 1/10 = 2/10 = 1/5

a,

\(5^{x+4}-3.5^{x+3}=2.5^{11}\)

\(\Rightarrow5^{x+3}\left(5-3\right)=2.5^{11}\)

\(\Rightarrow5^{x+3}2=2.5^{11}\)

\(\Rightarrow5^{x+3}=5^{11}\)

\(\Rightarrow x+3=11\)

\(\Rightarrow x=8\)

b, (Check lai xem de sai o dau khong nhe)

\(3.5^{x+2}+4.5^{x+3}=19.5^{10}\)

Dat 5x ra ben ngoai

\(\Rightarrow5^x.5^23+5^x:5^{-3}.4\)

\(\Rightarrow5^x\left(5^2.3+5^{-3}.4\right)\)

\(\Rightarrow5^x\left(5^{-3}.5^5.3+5^{-3}.4\right)\)

\(\Rightarrow5^x[5^{-3}\left(5^53+4\right)\)

\(\Rightarrow5^x[5^{-3}\left(3125.3+4\right)\)

\(\Rightarrow5^x\left(5^{-3}\right).9379\)

=> Khong tim duoc gia tri cua x \(\Rightarrow x\in\varnothing\)