TH 4.2. 1(Abel theory) 1)∑cn= converge at=≠0 →∑cn" absolutely converge on< n=0 2)∑cn" diverge at ∑cn- diverge on|> n=TH 4.2.1 (Abel theory) 0 0 0 0 1 0 1 0 1). converge at 0 absolutely converge on ; 2). diverge at diverge on . n n n n n n n n n n n n c z z c z z z c z z c z z z  =  =  =  =          1 z x y . O 0 z