数列复习课上有这样一例:ABC中,a,b,c成等差数列,求证:(1)B≤60°;(2)2cosA+2C=cosA2-C.在学生有足够的时间思考以后,提问学生甲:“如何证第(1)小题B≤60°?”学生甲的回答过程如下:∵a,b,c成等差数列,∴a+c=2b.∵sinaA=sinbB=sincc,∴sinAa++scinC=sinbB=2si2nbB,∴sinA+sinC= There is an example in the series review class: In ABC, a, b, c are equal arithmetic series. Proof: (1) B≤60°; (2) 2cosA+2C=cosA2-C. After students have enough time to think about , Question student A: “How to prove the (1) small question B ≤ 60 °?” Student A’s answer process is as follows: ∵a, b, c into an arithmetic series, ∴a+c=2b.∵sinaA=sinbB= Sincc, ∴sinAa++scinC=sinbB=2si2nbB, ∴sinA+sinC=