Add DLMF reference for acos
Add DLMF reference for acos

shipci/sympy,abhiii5459/sympy,pbrady/sympy,hargup/sympy,pandeyadarsh/sympy,sampadsaha5/sympy,atreyv/sympy,chaffra/sympy,dqnykamp/sympy,meghana1995/sympy,Gadal/sympy,Davidjohnwilson/sympy,grevutiu-gabriel/sympy,mcdaniel67/sympy,sampadsaha5/sympy,sahilshekhawat/sympy,VaibhavAgarwalVA/sympy,atsao72/sympy,kumarkrishna/sympy,Curious72/sympy,sahmed95/sympy,kumarkrishna/sympy,skirpichev/omg,Sumith1896/sympy,sunny94/temp,madan96/sympy,Titan-C/sympy,jerli/sympy,emon10005/sympy,pandeyadarsh/sympy,ChristinaZografou/sympy,bukzor/sympy,asm666/sympy,MechCoder/sympy,MechCoder/sympy,abloomston/sympy,asm666/sympy,wyom/sympy,beni55/sympy,cswiercz/sympy,kaichogami/sympy,toolforger/sympy,mafiya69/sympy,mcdaniel67/sympy,cccfran/sympy,vipulroxx/sympy,abhiii5459/sympy,cswiercz/sympy,atsao72/sympy,drufat/sympy,kumarkrishna/sympy,Gadal/sympy,jerli/sympy,debugger22/sympy,cccfran/sympy,lindsayad/sympy,saurabhjn76/sympy,abloomston/sympy,Mitchkoens/sympy,asm666/sympy,kaichogami/sympy,farhaanbukhsh/sympy,abloomston/sympy,Shaswat27/sympy,meghana1995/sympy,sunny94/temp,iamutkarshtiwari/sympy,yashsharan/sympy,sahilshekhawat/sympy,shipci/sympy,garvitr/sympy,shikil/sympy,beni55/sympy,drufat/sympy,cswiercz/sympy,souravsingh/sympy,atreyv/sympy,maniteja123/sympy,oliverlee/sympy,jamesblunt/sympy,wanglongqi/sympy,sahilshekhawat/sympy,Designist/sympy,Vishluck/sympy,aktech/sympy,grevutiu-gabriel/sympy,emon10005/sympy,jaimahajan1997/sympy,jbbskinny/sympy,oliverlee/sympy,sahmed95/sympy,sampadsaha5/sympy,jaimahajan1997/sympy,AkademieOlympia/sympy,souravsingh/sympy,toolforger/sympy,garvitr/sympy,jbbskinny/sympy,Sumith1896/sympy,mafiya69/sympy,drufat/sympy,skidzo/sympy,ga7g08/sympy,debugger22/sympy,liangjiaxing/sympy,saurabhjn76/sympy,dqnykamp/sympy,ChristinaZografou/sympy,chaffra/sympy,hargup/sympy,Mitchkoens/sympy,Titan-C/sympy,jaimahajan1997/sympy,ahhda/sympy,shipci/sympy,Vishluck/sympy,madan96/sympy,AunShiLord/sympy,yukoba/sympy,kaushik94/sympy,Shaswat27/sympy,pandeyadarsh/sympy,lindsayad/sympy,jamesblunt/sympy,toolforger/sympy,Sumith1896/sympy,ahhda/sympy,saurabhjn76/sympy,emon10005/sympy,oliverlee/sympy,ga7g08/sympy,grevutiu-gabriel/sympy,Arafatk/sympy,dqnykamp/sympy,wanglongqi/sympy,maniteja123/sympy,beni55/sympy,diofant/diofant,bukzor/sympy,kevalds51/sympy,aktech/sympy,debugger22/sympy,maniteja123/sympy,Arafatk/sympy,aktech/sympy,AunShiLord/sympy,souravsingh/sympy,moble/sympy,jbbskinny/sympy,abhiii5459/sympy,farhaanbukhsh/sympy,Davidjohnwilson/sympy,rahuldan/sympy,vipulroxx/sympy,sahmed95/sympy,AkademieOlympia/sympy,wanglongqi/sympy,Davidjohnwilson/sympy,Arafatk/sympy,MridulS/sympy,postvakje/sympy,wyom/sympy,skidzo/sympy,ChristinaZografou/sympy,Shaswat27/sympy,moble/sympy,rahuldan/sympy,liangjiaxing/sympy,VaibhavAgarwalVA/sympy,chaffra/sympy,wyom/sympy,vipulroxx/sympy,atreyv/sympy,meghana1995/sympy,moble/sympy,cccfran/sympy,MridulS/sympy,lindsayad/sympy,Mitchkoens/sympy,farhaanbukhsh/sympy,kaushik94/sympy,mcdaniel67/sympy,MridulS/sympy,liangjiaxing/sympy,jerli/sympy,kevalds51/sympy,jamesblunt/sympy,pbrady/sympy,shikil/sympy,bukzor/sympy,ga7g08/sympy,Titan-C/sympy,ahhda/sympy,skidzo/sympy,kevalds51/sympy,Curious72/sympy,garvitr/sympy,Designist/sympy,AkademieOlympia/sympy,postvakje/sympy,yukoba/sympy,yashsharan/sympy,yashsharan/sympy,Designist/sympy,mafiya69/sympy,AunShiLord/sympy,rahuldan/sympy,sunny94/temp,Vishluck/sympy,kaichogami/sympy,VaibhavAgarwalVA/sympy,postvakje/sympy,MechCoder/sympy,yukoba/sympy,hargup/sympy,shikil/sympy,pbrady/sympy,atsao72/sympy,iamutkarshtiwari/sympy,Gadal/sympy,kaushik94/sympy,madan96/sympy,iamutkarshtiwari/sympy,Curious72/sympy