Câu 3 !"#$"%&'()*+, /01234567891+,%:%;%<# = >=?@$A B Ct π π + -# D >=? D @$A B=D-t π π + 5E0FG:2H %,>?% I5==BDA@65=BJ@5=BK@L5FBDA@ M<2N0O "P #># = Q# D >=?@$AπRFπBS- %M)=?5 T4>?M8):ϕ>RFπBS U2N0O% #>FV?% #>=?@$AπRFπBS->F>VAπRFπBS>RπBC>V>=BK@ ! 0)%49W5 RπBC RFπBS F=?