a) \(7,5.x:\left(8-\frac{118}{21}\right)=\frac{43}{15}\)

\(\frac{15}{2}.x:\frac{50}{21}=\frac{43}{15}\)

\(\frac{15}{2}.x.\frac{21}{50}=\frac{43}{15}\)

\(\frac{63}{20}.x=\frac{43}{15}\)

\(x=\frac{43}{15}:\frac{63}{20}\)

\(x=\frac{172}{189}\)

b) \(3.\left(x-\frac{1}{2}\right)-2.\left(x+1\right)=1,25.x-1\)

\(3x-\frac{3}{2}-2x-2=\frac{5}{4}.x-1\)

\(\Rightarrow3x-2x-\frac{5}{4}x=(-1)+\frac{3}{2}+2\)

\(x.\left(3-2-\frac{5}{4}\right)=\frac{5}{2}\)

\(x.\frac{\left(-1\right)}{4}=\frac{5}{2}\)

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

\(x=-10\)

a: \(-3\frac12x-0,75-1,25x=\left(-\frac12\right)^2:\frac{-3}{4}+\frac16\)

=>\(-3,5x-1,25x=\frac14\cdot\frac{4}{-3}+\frac16+\frac34\)

=>\(-4,75x=\frac{-1}{3}+\frac16+\frac34=\frac{-4}{12}+\frac{2}{12}+\frac{9}{12}=\frac{-4+11}{12}=\frac{7}{12}\)

=>\(x=\frac{7}{12}:\frac{-19}{4}=\frac{7}{12}\cdot\frac{-4}{19}=\frac{-7}{3\cdot19}=-\frac{7}{57}\)

b: \(-\frac23-\left(\frac{x}{2}-75\%\right)=\left(\frac{3}{-4}-\frac98\right)^2:\frac{-3}{32}-1\frac13\)

=>\(-\frac23-0,5x+\frac34=\left(-\frac68-\frac98\right)^2\cdot\frac{-32}{3}-\frac43\)

=>\(-0,5x+\frac{1}{12}=\left(-\frac{15}{8}\right)^2\cdot\frac{-32}{3}-\frac43\)

=>\(-0,5x+\frac{1}{12}=\frac{225}{64}\cdot\frac{-32}{3}-\frac43=\frac{-75}{2}-\frac43=\frac{-225-8}{6}=\frac{-231}{6}\)

=>\(-0,5x=-\frac{231}{6}-\frac{1}{12}=\frac{-462-1}{12}=\frac{-463}{12}\)

=>\(x=\frac{463}{12}:0,5=\frac{463}{12}:\frac12=\frac{463}{12}\cdot2=\frac{463}{6}\)

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

\(\frac{1}{2}x-\frac{3}{8}-\frac{2}{5}x=4\frac{1}{4}\)

\(\frac{1}{10}x=\frac{17}{4}+\frac{3}{8}\)

\(\frac{1}{10}x=\frac{37}{8}\)

\(x=\frac{185}{4}\)

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

\(\frac{1}{2}x-\frac{3}{8}-\frac{2}{5}x=\frac{17}{4}\)

\(\frac{1}{2}x-\frac{2}{5}x=\frac{17}{4}+\frac{3}{8}\)

\(\frac{1}{10}x=\frac{37}{8}\)

       \(x=\frac{37}{8}:\frac{1}{10}\)

      \(x=\frac{185}{4}\)

ta có ;

1+2+3+...+x= x(x+1)/2 

=)x(x+1)/2=8001

=)x(x+1)=16002

Phân tích ra thừa số nguyên tố : 16002=126x127

=) x(x+1)=216x217

=) x=216

vây x=216

SSH:(x-1):1=1=80001 số

Tổng tương tự, ta có:

(x+1).x:2=8001.2

Kết quả x là:

(x+1).x=8001:2=16002=127.126

Vậy x=126

b)

\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{2}{x.\left(x+1\right)}=\frac{2007}{2009}\)

\(=\frac{1}{1.3}+\frac{1}{2.3}+\frac{1}{2.5}+...+\frac{2}{x.\left(x+1\right)}=\frac{2007}{2009}\)

\(=\frac{1}{2}.\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x.\left(x+1\right)}\right)=\frac{2007}{2009}\)

\(=\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{2007}{2009}:\frac{1}{2}\)

\(=\frac{1}{2}-\frac{1}{x+1}=\frac{2007}{4018}\)

\(=\frac{1}{x-1}=\frac{1}{2009}\Leftrightarrow x+1=2009\)

\(\Rightarrow x=2009-1=2008\)

Bạn Phúc Trần Tấn bạn có biết làm phần a ko?Giúp mk với ạ!Mai mk cần rùi

Bai giai: 

a) do x-3|x-5|=0 nen x-3 hoac |x-5|=0

* x-3=0=>x=3

* |x-5|=0=>x-5=0=>x=5

Vay x=3 hoac x=5

b) tich roi lam cho

hello bình

bạn này https://olm.vn/thanhvien/nganhatbinhvy  xàm loz, người ta đăng câu hỏi, giải k giải mà ...

Ta có : \(\left|3-x\right|=x-5\)

\(\Leftrightarrow\orbr{\begin{cases}x-3=x-5\\x-3=5-x\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x-x=-5+3\\x+x=5+3\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}0x=-2\left(loại\right)\\2x=8\end{cases}}\)

=> x = 4