【春季】四年級(jí)創(chuàng)新班第2講:等差數(shù)列的應(yīng)用佩奇老師 <p class="ql-block">第2講：等差數(shù)列的應(yīng)用</p><p class="ql-block">在等差數(shù)列中：</p><p class="ql-block">公差表示后一個(gè)數(shù)與前一個(gè)數(shù)的差。</p><p class="ql-block">首項(xiàng)表示第一個(gè)數(shù)</p><p class="ql-block">末項(xiàng)表示最后一個(gè)數(shù)</p><p class="ql-block">項(xiàng)數(shù)表示數(shù)的個(gè)數(shù)</p><p class="ql-block"><br></p><p class="ql-block">等差數(shù)列總和=(首項(xiàng)+末項(xiàng))ⅹ項(xiàng)數(shù)÷2 </p><p class="ql-block">當(dāng)項(xiàng)數(shù)為奇數(shù)個(gè)時(shí)，總和=中心數(shù)x項(xiàng)數(shù) </p><p class="ql-block">末項(xiàng)=首項(xiàng)+(項(xiàng)數(shù)-1)x公差</p><p class="ql-block">公差=(未項(xiàng)-首項(xiàng))÷(項(xiàng)數(shù)-1)</p><p class="ql-block">項(xiàng)數(shù)=(未項(xiàng)-首項(xiàng))÷公差+1</p><p class="ql-block">首項(xiàng)=末項(xiàng)-公差??（項(xiàng)數(shù)?1）</p> 項(xiàng)數(shù)首項(xiàng)公差等差數(shù)列數(shù)末項(xiàng)末項(xiàng)未項(xiàng)數(shù)項(xiàng)總和表示