Find the indefinite integrals.

$($a$)(10$ points$)$

${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{1}{\sqrt[\phantom{2}]{1-4x^2}}dx$

$($b$)(10$ points$)$

${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{x}{x^4+25}dx$

$($c$)(10$ points$)$

${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{x^6}{(5+x^7{)}^3}dx$