题目

阅读理解 While elephants born without tusks (长牙)are not unheard of，they normally form just 2 to 6 percentof the population. However, that is not the case at Mozambique's GorongosaNational Park, where an astonishing 33 percent of female elephants born afterthe country's civil war ended in 1992 are tuskless. While that may appear to bejust a coincidence, Joyce Poole, an elephant behavior expert, has anothertheory. The researcher thinks we may be witnessing unnatural evolution of thespecies due to the constant hunting of elephants for valuable ivory. Poole says before the country's15-ye已知数列{an}中，（n∈N*）．（1）证明数列{nan}（n≥2）为等比数列；（2）求数列{n2an}的前n项和Tn．