Valencia is in the east part of Spain(西班牙). It has a port on the sea, two miles away on the coast. It is the capital of a province that is also named Valencia. The city is a market centre for
The time he has devoted in the past years _______ the disable is now considered ________ of great value. A. to help; being B. to helping; to be C. to help; to be D. helping; be
的前
项和为
，
．已知
，
，
，且当
时，
．
求
的值；
证明：
为等比数列；
求数列
；（2）证明见解析；（3）
．
