锡枸app

莫波何2625锡有三种同素异形体:灰锡(a锡)、白锡(b锡)和脆锡. - 上学吧普法考试
裘姬真17280956235 ______ 由an=Sn-S(n-1),可得 Sn-2S(n-1)=2^n →Sn/2^n-S(n-1)/2^(n-1)=1 →{Sn/2^n}是以3/2为首项,1为公差的等差数列 →Sn/2^n=(n+2)/2 →Sn=(2n+1)*2(n-1) an=Sn-S(...