C h o h a ˋ m s o ^ ˊ f ′ ( x ) = ( 2 x + 1 ) ⋅ f 2 ( x ) v a ˋ f ( 1 ) = − 0 , 5. T ổ n g f ( 1 ) + f ( 2 ) + f ( 3 ) + … + f ( 2017 ) + f ( 2018 ) + f ( 2019 ) + f ( 2020 ) = b a ; ( a ∈ ◻ ; b ∈ ◻ ) v ớ i b a t o ^ ˊ i g i ả n . K h ẳ n g đ ị nh n a ˋ o s a u đ a ^ y đ u ˊ n g ?