acos(7*x)
d --(acos(7*x)) dx
-7 -------------- ___________ / 2 \/ 1 - 49*x
-343*x -------------- 3/2 / 2\ \1 - 49*x /
/ 2 \ | 147*x | -343*|1 + ---------| | 2| \ 1 - 49*x / -------------------- 3/2 / 2\ \1 - 49*x /