If a/b + b/a = 2, then the value of (a - b) is = ?

Answer: Option D

$$\begin{array}{rl}& \text{Given,}\frac{a}{b}\text{ + }\frac{b}{a}\text{ = 2}\\ & \Rightarrow \frac{a^2+b^2}{ab}=2\\ & \Rightarrow a^2+b^2=2ab\\ & \Rightarrow a^2+b^2-2ab=0\\ & \Rightarrow {\left(a-b\right)}^2=0\\ & \Rightarrow \left(a-b\right)\text{ = 0 }\end{array}$$