Toán học
... Btngthcchotngngvibtngthcsau: ( )BbcCacAabcba2222sinsinsin4 + + + + ( ) ( ) ( )02cos22cos22cos22cos122cos122cos12222222222 + + + + + - + - + - + + + + + CacBbcAabcbaBcbCcaAbaabcabcba ... 1t1tan1 = a , 1 - = b khiú 2,1 = "n tacú:nnSn b a + = tanVybitoỏncchngminhvistnticacỏchngs b a, nhtrờnBi9:Dóysxỏcnhnhsau: ù ợ ù ớ ỡ - = = +12210nnxxaxn=0,1,2...