let f2 be PartFunc of REAL,REAL; :: thesis: for A being non empty closed_interval Subset of REAL st A c= ].(- 1),1.[ & dom (arccos `| ].(- 1),1.[) = dom f2 & ( for x being Real holds
( x in ].(- 1),1.[ & f2 . x = - (1 / (sqrt (1 - (x ^2)))) ) ) & f2 | A is continuous holds
integral (f2,A) = (arccos . (upper_bound A)) - (arccos . (lower_bound A))
let A be non empty closed_interval Subset of REAL; :: thesis: ( A c= ].(- 1),1.[ & dom (arccos `| ].(- 1),1.[) = dom f2 & ( for x being Real holds
( x in ].(- 1),1.[ & f2 . x = - (1 / (sqrt (1 - (x ^2)))) ) ) & f2 | A is continuous implies integral (f2,A) = (arccos . (upper_bound A)) - (arccos . (lower_bound A)) )
assume that
A1: A c= ].(- 1),1.[ and
A2: dom (arccos `| ].(- 1),1.[) = dom f2 and
A3: for x being Real holds
( x in ].(- 1),1.[ & f2 . x = - (1 / (sqrt (1 - (x ^2)))) ) and
A4: f2 | A is continuous ; :: thesis: integral (f2,A) = (arccos . (upper_bound A)) - (arccos . (lower_bound A))
A5: A c= dom f2 by A1, A2, FDIFF_1:def 7, SIN_COS6:106;
A6: dom (arccos `| ].(- 1),1.[) = ].(- 1),1.[ by FDIFF_1:def 7, SIN_COS6:106;
for x being Element of REAL st x in dom (arccos `| ].(- 1),1.[) holds
(arccos `| ].(- 1),1.[) . x = f2 . x

proof

let x be Element of REAL ; :: thesis: ( x in dom (arccos `| ].(- 1),1.[) implies (arccos `| ].(- 1),1.[) . x = f2 . x )
assume A7: x in dom (arccos `| ].(- 1),1.[) ; :: thesis: (arccos `| ].(- 1),1.[) . x = f2 . x
then A8: ( - 1 < x & x < 1 ) by A6, XXREAL_1:4;
(arccos `| ].(- 1),1.[) . x = diff (arccos,x) by A6, A7, FDIFF_1:def 7, SIN_COS6:106
.= - (1 / (sqrt (1 - (x ^2)))) by A8, SIN_COS6:106
.= f2 . x by A3 ;
hence (arccos `| ].(- 1),1.[) . x = f2 . x ; :: thesis: verum

end;

then A9: arccos `| ].(- 1),1.[ = f2 by A2, PARTFUN1:5;
f2 is_integrable_on A by A6, A1, A2, A4, INTEGRA5:11;
hence integral (f2,A) = (arccos . (upper_bound A)) - (arccos . (lower_bound A)) by A1, A4, A5, A9, INTEGRA5:10, INTEGRA5:13, SIN_COS6:106; :: thesis: verum