28. Suppose $a \neq 0, b \neq 0, c \neq 0$ and $\frac{0}{b}=\frac{b}{c}=\frac{1}{a}$. Find the value of $\frac{a+b-c}{a-b+c}$.
28 Ans: 1 .
Letting $\frac{a}{b}=k$, we get $a=b k, b=c k$ and $c=a k$. Thus $a=a k^{3}$. Thus $k=1$ and $a=b=c$. The result follows.