Let's take the limit $$\lim_{x \to \infty} \left(x + y\right)^{2}$$ Let's divide numerator and denominator by x^2: $$\lim_{x \to \infty} \left(x + y\right)^{2}$$ = $$\lim_{x \to \infty}\left(\frac{1 + \frac{2 y}{x} + \frac{y^{2}}{x^{2}}}{\frac{1}{x^{2}}}\right)$$ Do Replacement $$u = \frac{1}{x}$$ then $$\lim_{x \to \infty}\left(\frac{1 + \frac{2 y}{x} + \frac{y^{2}}{x^{2}}}{\frac{1}{x^{2}}}\right) = \lim_{u \to 0^+}\left(\frac{u^{2} y^{2} + 2 u y + 1}{u^{2}}\right)$$ = $$\frac{0^{2} y^{2} + 2 \cdot 0 y + 1}{0} = \infty$$
The final answer: $$\lim_{x \to \infty} \left(x + y\right)^{2} = \infty$$
Lopital's rule
There is no sense to apply Lopital's rule to this function since there is no indeterminateness of 0/0 or oo/oo type
Other limits x→0, -oo, +oo, 1
$$\lim_{x \to \infty} \left(x + y\right)^{2} = \infty$$ $$\lim_{x \to 0^-} \left(x + y\right)^{2} = y^{2}$$ More at x→0 from the left $$\lim_{x \to 0^+} \left(x + y\right)^{2} = y^{2}$$ More at x→0 from the right $$\lim_{x \to 1^-} \left(x + y\right)^{2} = \left(y + 1\right)^{2}$$ More at x→1 from the left $$\lim_{x \to 1^+} \left(x + y\right)^{2} = \left(y + 1\right)^{2}$$ More at x→1 from the right $$\lim_{x \to -\infty} \left(x + y\right)^{2} = \infty$$ More at x→-oo