x = 2 \cdot sin u

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d x = 2 \cdot cos u d u

\int \frac{2 sin u}{\sqrt{4 - 4 {sin}^{2} u}} \cdot 2 cos u d u

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= \int \frac{2 sin u \cdot 2 cos u}{2 \sqrt{1 - {sin}^{2} u}} d u

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= \int \frac{2 sin u \cdot cos u}{cos u} d u

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= \int 2 sin u d u

= - 2 cos u + C

$= - 2 \sqrt{1 - {sin}^{2} u} + C$ .
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$= - 2 \sqrt{1 - {(\frac{x}{2})}^{2}} + C$ .