$$\frac{a^2}{b^2}+\frac{b^2}{a^2}+2$$
$$=\frac{a^4+b^4+2a^2b^2}{a^2b^2}.$$
$$=\frac{\left(a^2+b^2\right)^2}{a^2b^2}.$$
So,
$$\sqrt{\frac{a^2}{b^2}+\frac{b^2}{a^2}+2}=\frac{\left(a^2+b^2\right)}{ab}=\left(\frac{a}{b}+\frac{b}{a}\right).$$
D is correct choice.
Create a FREE account and get: