Definite Integral of Reciprocal of Root of a Squared minus x Squared

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Theorem

$\ds \int_0^x \frac {\d t} {\sqrt{1 - t^2} } = \arcsin x$

Proof

\(\ds \int_0^x \frac {\d t} {\sqrt{1 - t^2} }\)

\(=\)

\(\ds \intlimits {\arcsin \frac t 1} 0 x\)

Primitive of $\dfrac 1 {\sqrt {a^2 - x^2} }$, Definition of Definite Integral

\(\ds \)

\(=\)

\(\ds \arcsin x - \arcsin 0\)

\(\ds \)

\(=\)

\(\ds \arcsin x\)

$\blacksquare$

Sources

• 1992: George F. Simmons: Calculus Gems ... (previous) ... (next): Chapter $\text {A}.33$: Weierstrass ($\text {1815}$ – $\text {1897}$)