\(4x^3-3=29\Leftrightarrow4x^3=32\Leftrightarrow x=2\).

\(\frac{y-25}{-16}=\frac{z+49}{25}=\frac{x+16}{9}=\frac{2+16}{9}=2\)

\(\Leftrightarrow\hept{\begin{cases}y-25=2.\left(-16\right)=-32\\z+49=2.25=50\end{cases}}\Leftrightarrow\hept{\begin{cases}y=-7\\z=1\end{cases}}\)

\(A=x-2y+3z=2+14+3=19\)

Có nha

Cs nha bạn 

\(MS=\frac{2019}{1}+\frac{2018}{2}+\frac{2017}{3}+...+\frac{1}{2019}\)

\(=1+1+\frac{2018}{2}+1+\frac{2017}{3}+...+1+\frac{1}{2019}\)

\(=\frac{2020}{2020}+\frac{2020}{2}+\frac{2020}{3}+...+\frac{2020}{2019}\)

\(=2020\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2020}\right)\)

Suy ra \(D=\frac{1}{2020}\).

(7x-14)^2=25

<=>7x-14=5 hoặc 7x-14=-5

TH1:7x-14=5->7x=5+14=19-->x=19/7(thỏa mãn x thuộc Q)

TH2:7x-14=-5-->7x=-5+14=9-->x=9/7(thỏa mãn x thuộc Q)

chúc bạn học tốt!

b) \(\left|x-\frac{3}{4}\right|+\left|\frac{2}{5}-y\right|+\left|x-y+z\right|=0\)

\(\Leftrightarrow\hept{\begin{cases}x-\frac{3}{4}=0\\\frac{2}{5}-y=0\\x-y+z=0\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}x=\frac{3}{4}\\y=\frac{2}{5}\\z=-\frac{7}{20}\end{cases}}\).

a), c) Tương tự. 

\(\frac{x}{y}=\frac{3}{4}\Leftrightarrow\frac{x}{3}=\frac{y}{4}\Leftrightarrow\frac{x}{15}=\frac{y}{20}\)

\(\frac{y}{z}=\frac{5}{7}\Leftrightarrow\frac{y}{5}=\frac{z}{7}\Leftrightarrow\frac{y}{20}=\frac{z}{28}\).

Suy ra \(\frac{x}{15}=\frac{y}{20}=\frac{z}{28}\).

Áp dụng tính chất dãy tỉ số bằng nhau ta có: 

\(\frac{x}{15}=\frac{y}{20}=\frac{z}{28}=\frac{2x+3y-z}{2.15+3.20-28}=\frac{186}{62}=3\)

\(\Leftrightarrow\hept{\begin{cases}x=3.15=45\\y=3.20=60\\z=3.28=84\end{cases}}\).