【简答题】设数列{ a n }满足 a 1 =2, a 2 + a 4 =8,且对任意 n ∈N * ,函数 f ( x )=( a n - a n +1 + a n +2 ) x + a n +1 cos x - a n +2 sin x 满足 f ′ =0. (1)求数列{ a n }的通项公式; (2)若 b n =2 ,求数列{ b n }的前 n 项和 S n .
【简答题】设数列{a n }满足a 1 =2,a 2 +a 4 =8,且对任意n∈N * ,函数f(x)=(a n -a n+1 +a n+2 )x+a n+1 cos x-a n+2 sin x满足f′ =0. (1)求数列{a n }的通项公式; (2)若b n =2(a n + ),求数列{b n }的前n项和S n .