Given $a\in\mathbb{R}^2\backslash X$ and $v\in\mathbb{R}^2$, $\exists\delta$ such that $t\in[0,\delta) \Rightarrow a+tv\in...

Given $a\in\mathbb{R}^2\backslash X$ and $v\in\mathbb{R}^2$,
$\exists\delta$ such that $t\in[0,\delta) \Rightarrow a+tv\in...

Let $X=\{(x,y)\in\mathbb{R}^2;\;x>0 \;\text{and}\;x^2\leq y\leq2x^2\}$.
Prove that for all $(a,v)\in(\mathbb{R^2}\backslash X)\times \mathbb{R}^2$
there exists $\delta>0$ such that $$0\leq t <\delta \Rightarrow a+tv\in
\mathbb{R}^2\backslash X$$
This problem is in the section of differentiable functions of my book.
Thanks.