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\(450:\left(x-19\right)=50\\ \Leftrightarrow x-19=5\\ \Leftrightarrow x=24\)
\(2\left(x-52\right)=2.23+20\\ \Leftrightarrow2\left(x-52\right)=66\\ \Leftrightarrow x-52=33\\ \Leftrightarrow x=85\)
\(10-\left(x-3\right):2=72-100\\ \Leftrightarrow10-\left(x-3\right):2=-28\\ \Leftrightarrow10-\left(x-3\right)=-56\\ \Leftrightarrow x-3=66\\ \Leftrightarrow x=69\)
1.x-19=450:50
x-19=9
x =9+19
x =28
2. 2(x-51)=46+20
2(x-51)=66
x-51=66:2
x-51=33
x =33+51
x =84

\(x_1+x_2+x_3+........+x_{49}+x_{50}+x_{51}=0\)
\(\Rightarrow\left(x_1+x_2\right)+\left(x_3+x_4\right)+...........+\left(x_{49}+x_{50}\right)+x_{51}=0\)
Theo bài ra ta có: \(1+1+1+.......+1+x_{51}=0\) \(\Rightarrow1\times25+x_{51}=0\) \(\Rightarrow x_{51}=-25\)
mà \(x_{50}+x_{51}=0\Rightarrow x_{50}+\left(-25\right)=1\Rightarrow x_{50}=26\)

\(\left(\frac{24}{5}+x+50\right):\frac{2}{3}\)\(=-51\)
\(\left(\frac{24}{5}+x+50\right)\)\(=-51.\frac{2}{3}\)
\(\left(\frac{24}{5}+x+50\right)\)\(=-34\)
\(\frac{24}{5}\)\(+x\)\(=-34-50\)
\(\frac{24}{5}\)\(+x\)\(=-84\)
\(x=-84-\frac{24}{5}\)
\(x=-88,8\)


24 hay là 2( số nhân với mẫu rồi cộng tử) rùi đến 4 phần 5

\(\left(2\frac{4}{5}.x-50\right):\frac{2}{3}=51\)
\(\Leftrightarrow\)\(\frac{14}{5}.x-50=51.\frac{2}{3}=34\)
\(\Leftrightarrow\)\(\frac{14}{5}x=34+50=84\)
\(\Leftrightarrow\)\(x=84:\frac{14}{5}=30\)
Vậy....
\(\left(2\frac{4}{5}x-50\right):\frac{2}{3}=51\)
\(\left(\frac{14}{5}x-50\right)=51\times\frac{2}{3}\)
\(\left(\frac{14}{5}x-50\right)=34\)
\(\frac{14}{5}x=34+50\)
\(\frac{14}{5}x=84\)
\(x=84:\frac{14}{5}\)
\(x=30\)

Bài toán sai
bài toán đúng là x+(x+1)+(x+2)+(x+3)+...+19+20=20

b){x-[52+(35-80.3)3-51]50+14}=20
=>x-[25+(243-240)3-51]50+14=20
=>x-[25+33-51]50+14=20
=>x-[25+27-51]50+14=20
=>x-[52-51]50+14=20
=>x-150+14=20
=>x-1+14=20
=>x-1=20-14
=>x-1=6
=>x=6+1
=>x=7

ta có : x1 +x2 +x3 +...+x50 = 1*25=25
suy ra : x51 =0-25=-25
mà x50+x51=1
suy ra x50= 1-(-25)=26