If x/a = 1/a - 1/x , then the value of x - x2 is?

Answer: Option C

$$\begin{array}{rl}& \frac{x}{a}=\frac{1}{a}-\frac{1}{x}\\ & \Rightarrow \frac{x}{a}-\frac{1}{a}=-\frac{1}{x}\\ & \Rightarrow \left(\frac{x-1}{a}\right)=-\frac{1}{x}\\ & \Rightarrow \frac{1-x}{a}=\frac{1}{x}\\ & \Rightarrow x\left(1-x\right)=a\\ & \Rightarrow x-x^2=a\end{array}$$