资源描述
单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,数学必修五,授课人:李玲,等差数列的性质,在如下的两个数之间,插入一个什么数后这三个,数就会成为一个等差数列:,(,1,),2,,,(),,,4,(,2,),-12,,,(,),,,0,(3),(),如果在,a,与,b,中间插入一个数,A,,使,a,,,A,,,b,成等差数列,那么,A,叫做,a,与,b,的,等差中项,。,3,-6,探究,1,a,2,a,3,a,4,a,5,a,6,a,7,a,8,-6,-10,a,n,为等差数列,请填写表格,观察项之间的数量关系,回答下列问题。,(,1,),a,5,是哪些项的等差中项?与,a,1,a,9,之间有什么关系?请用数,学表达式写出它们的数量关系。,(,2,)观察各项的下标,你能否用数学语言描述(,1,)中的规律?,(,3,)既然都和,a,5,有关,那么,a,4,,,a,6,与,a,3,,,a,7,有什么关系?,(,4,)观察各项的下标,你能否用数学语言描述(,2,)中的规律?,(,5,)对于所有的等差数列是否都满足这种关系呢?,-4,-8,-12,-2,-14,探究,2,a,2,a,3,a,4,a,5,a,6,a,7,a,8,-2,-4,-6,-10,-14,a,n,为等差数列,请填写表格,观察项之间的数量关系,回答下列问题。,(,6,)请问,a,3,,,a,5,,,a,7,a,2,,,a,5,,,a,8,a,1,,,a,3,,,a,5,a,7,a,9,是否,是等差数列?若是公差是多少?公差与下标之间,满足什么关系?,-8,-12,探究,2,等差数列性质,?,?,例:,a,2,a,8,=,例:,a,2,a,8,=,a,3,+,题型一:等差数列性质的应用,已知等差数列,a,n,中,(1),a,2,a,8,a,14,1,,求,a,3,a,13,;,(2),已知,a,2,a,3,a,23,a,24,48,,求,a,13,;,(3),已知,a,2,a,3,a,4,a,5,34,,,a,2,a,5,52,,求公差,d,.,(1),三个数成等差数列,和为,6,,积为,24,,求这三个数,(,2,)已知成等差数列的四个数之和为,26,,第二个数与第三个数之积为,40,,求这个等差数列,题型二:等差数列性质的运算,小结,a,n,为等差数列,课后作业,1.,已知等差数列,a,n,中,,a,3,a,15,是方程,x,2,-6x-1=0,的两根,则,a,7,+a,8,+a,9,+a,10,+a,11,=_.,2.,在等差数列,a,n,中,,a,1,+a,2,=3,,,a,1,+a,2,+a,3,+a,4,=10,,则,a,1,+a,2,+a,3,+a,4,+a,5,+a,6,=_,。,3,在等差数列数列,a,n,中,,a,3,+a,5,+a,7,+a,9,+a,11,100,,求,3a,9,a,13,的值,
展开阅读全文