Find the Derivative

$\displaystyle y = 2 \arcsin \sqrt{1 - 2x}$

using the formula for derivative of arcsin:

$\displaystyle \frac{d}{dx}\sin^{-1} $

and

$\displaystyle u = (\frac{1}{\sqrt{1 - u^{2}}})(\frac{du}{dx})$

Step 1.

$\displaystyle y = 2[\frac{1}{\sqrt{1-(\sqrt{1-2x})^{2}}}] [\frac{1}{2}(1-2x)^{-1/2}](-2)$

Step 2:

Can't understand how they get from here (below this sentence) to the answer.

$\displaystyle y = (\frac{1}{\sqrt{1-1+2x}})(\frac{1}{\sqrt{1-2x}})(-2)$

Answer:

$\displaystyle y = \frac{-2}{\sqrt{2x - 4x^{2}}}$