+1252 I don't want to tell you the full answer, but I'll start you off.
Multiply both sides by x and get \(\sqrt{1-4x^2}-1 \geq -4x\).
To get rid of the radical, we can move all radical signs to the left and non-radicals to the right.
This is what we'll do here.
\(\sqrt{1-4x^2} \geq -4x+1\).
Now square both sides, and then you probably know what to do from there.
You are very welcome!
:P
start by multiplying by x both sides to get
\(\sqrt{1-4x^2}-1\) _> equal or more than, -4x
Now add 1
\(\sqrt{1-4x^2}\) _> equal or more than -4x+1
Square both sides
1-4x^2_> equal or more than (-4x+1)^2
subtract 1
-4x^2_>equal or more than (-4x+1)^2 -1
divide by -4(Note we reverse the inequality sign)
x^2_< equal or less than ((-4x+1)^2-1)/-4 (All divided by -4)
now square root both sides
x _< equal or less than sqrt((-4x+1)^2-1)/-4))
+118677 Note: I have a=had to edit this a number of times becasue the LaTex compiler is playing up.
It keeps deleting things. 
\(\frac{\left(\sqrt{1-4x^2}-1\right)}{x}\ge -4\)
I will look at the domain restrictions first.
I am assuming that you want only real answers.
\(1-4x^2\ge0\\ 1\ge4x^2\\ 4x^2\le1\\ (2x)^2\le1\\ -1\le2x\le1\\ -0.5\le x\le0.5 \)
Oh, I canot divide by zero either so x cannot be zero
\(-0.5\le x<0 \qquad \)
or \(0< x<0.5\)
Now that I have an initial restriction for x values I will look at the rest.
You cannot just multiply by x as Coolstuff has done because you do not know if x is positive or negative and if it is negative the sign has to be turned around.
Normally the easiest way to handle these is to multiply through by x^2 because we know that x^2 has to be positive. But in this case that will work well.
SO
When is
\(\sqrt{1-4x^2}-1> 0\\ \sqrt{1-4x^2}>1\\ 1-4x^2>1\\ -4x^2>0\\ NO\;\;solutions.\)
If I had thought about it before hand I could have seen that this was the case.
So
\(\sqrt{1-4x^2}-1\le0\qquad \text{for all values of x}\)
If x is negative then the LHS of the original inequality will always be positive so the LHS will always be bigger than -4
So all values of x where \(-0.5\le x < 0\) will make the equation true.
--------------------------------
If x is positive then
\(\frac{\left(\sqrt{1-4x^2}-1\right)}{x}\ge -4\\ \sqrt{1-4x^2}-1\ge -4x\\ \sqrt{1-4x^2}\ge -4x+1\\ \qquad If\;\;-4x+1<0\quad \text{then this must be true}\\ \qquad If\;\;-4x<-1\quad \text{then this must be true}\\ \qquad If\;\;x>-0.25\quad \text{then this must be true}\\ \qquad \text{Since I am only looking at positive values of x, x must be greater than -0.25}\)
So the solution set is [-0.5, 0) union (0, 0.5]
