You cannot square root -4... why/how are you even at a point where you need to do that??
Also, I would
not advise you to just 'square root both sides of the inequality'
If you do so, then you'd end up with
x≤2. This is not the correct answer, and rather just one half of it. The reason why is simply because if you take
x=−6 which satisfied the inequality, you do not get that
x2≤4 which is the original requirement!