已知等差数列的前项和为,若,,( 且). (1)求的值; (2)若数列满足,求数列的前项和. 答案:(1)由已知得:, 且, 设数列的公差为,则有, ∴, 由,得,即 ∴ ∴ (2)由(1)知,,,∴, ∴,得. ∴ 设数列的前项和为 ∴① ② ①–②,得: ∴() 3. The surface of Mars is like the surface of the Earth than planet in the solar system. A. much;the other B. much;any other C. more;the other D. more;any other