a)

\(\dfrac{x}{2}=\dfrac{y}{3};\dfrac{y}{4}=\dfrac{z}{5}\)

\(\Rightarrow\dfrac{x}{8}=\dfrac{y}{12};\dfrac{y}{12}=\dfrac{z}{15}\)

\(\Rightarrow\dfrac{x}{8}=\dfrac{y}{12}=\dfrac{z}{15}\)

\(\Rightarrow\dfrac{x^2}{64}=\dfrac{y^2}{144}=\dfrac{z^2}{225}\)

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

\(\dfrac{x^2}{64}=\dfrac{y^2}{144}=\dfrac{x^2-y^2}{64-144}=\dfrac{16}{-80}=\dfrac{1}{-5}\)

Vì \(x^2;y^2;z^2\ge0\) nên không tồn tại 3 số cần tìm

1/2+1/4+1/8+1/10+1/16+1/32+1/64+1/128

=1-1/2+1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/16+1/16-1/32+1/32-1/64+1/64-1/128+1/128

=1-1/128

=127/128

#Sagittarius#

A ) x = 5/24

B ) x = 7/15

\(\frac{1}{4}:\left(\frac{x}{4}+\frac{\left(-2\right)}{7}+\frac{2}{8}\right)=\frac{\left(-1\right)}{14}\)

\(\frac{1}{4}:\left(\frac{x}{4}+\frac{\left(-1\right)}{28}\right)=\frac{\left(-1\right)}{14}\)

\(\frac{x}{4}+\frac{\left(-1\right)}{28}=\frac{1}{4}:\frac{\left(-1\right)}{14}\)

\(\frac{x}{4}+\frac{\left(-1\right)}{28}=\frac{-7}{2}\)

\(\frac{x}{4}=\frac{-7}{2}-\frac{\left(-1\right)}{28}\)

\(\frac{x}{4}=\frac{-97}{28}\)

\(\frac{7x}{28}=\frac{-97}{28}\)

\(\Rightarrow7x=-97\)

\(\Rightarrow x=-97:7\)

\(\Rightarrow x=\frac{-97}{7}\)

Váy \(x=\frac{-97}{7}\)

Nhớ k cho mk nha  Le Ha Trang