Primitive of Reciprocal of Root of 1 minus x squared/Arcsine Form/Proof 1

Proof
From Primitive of $\dfrac 1 {\sqrt {a^2 - x^2} }$: Arcsine Form:
 * $\ds \int \frac {\d x} {\sqrt {a^2 - x^2} } = \arcsin \frac x a + C$

The result follows by setting $a = 1$.