Which notation/abbreviation is appropriate to denote logical implication while writing proofs/solutions?

Question

Find $x$ by solving the equation $$\frac{d (x^{2})}{dx} = 2$$

How should I write the remaining steps of the solution?

Should it be

$\implies 2x = 2$

$\implies x= 1$

OR

i.e. $2x=2$

i.e. $x=1$

OR

or $2x=2$

or $x=1$

OR

$\therefore 2x=2$

$\therefore x=1$

Which notations are appropriate?