Ta có :\(\frac{1}{2}a=2b\Rightarrow a=2b:\frac{1}{2}=2b\cdot2=4b\left(1\right)\)

Ta cũng có:\(\frac{9}{8}a=kb\left(2\right)\)

Thay (1) vào (2), ta có:

\(\frac{9}{8}\cdot4b=kb\)

\(\frac{9}{2}b=kb\)

\(\frac{9}{2}b:b=k\)

\(\frac{9}{2}\cdot1=k\)

\(\Rightarrow\frac{9}{2}=k\)

Vậy \(k=\frac{9}{2}\)

mình ấn kết quả đấy nhưng sai :((((

1/2 .a =2b 

Nhân 2 vế với 9/4

9/8 .a = 9/4 .2b =6b .3/4 =k.3/4

=> k = 6b

K=4,5

Nho tick nha

Tick di roi day trinh bay

\(\frac{1}{2}=2\Rightarrow\frac{1}{8}=\frac{1}{2}\Rightarrow\frac{9}{8}=\frac{9}{2}\Rightarrow k=\frac{9}{2}\)

\(\frac{1}{2}a=2b\Leftrightarrow\frac{a}{2}=2b\Leftrightarrow a=4b\left(1\right)\)

\(\frac{9}{8}a=bk\Leftrightarrow\frac{9a}{8}=bk\Leftrightarrow9a=8bk\Leftrightarrow a=\frac{8bk}{9}\left(2\right)\)

Từ (1) và (2) \(\Rightarrow4b=\frac{8bk}{9}\)

\(\Leftrightarrow4b\cdot9=8bk\)

\(\Leftrightarrow36b=8bk\)

\(\Leftrightarrow\frac{36b}{8b}=k\)

\(\Leftrightarrow k=\frac{9}{2}\)

Vậy......

Có: \(\frac{1}{2}.a=2b\Rightarrow a=4b\)

\(\frac{9}{8}.a=kb\)

\(\Rightarrow\frac{9}{8}.4b=kb\)

\(\frac{9}{2}b=kb\)

\(\Leftrightarrow k=\frac{9}{2}\)\(\left(b\ne0\right)\)

Vậy \(k=\frac{9}{2}\)

9/2                                  

\(\frac{9}{2}\)