設(shè){an}是一個(gè)公差為d（d不等于0）的等差數(shù)列，它的前10項(xiàng)和S10=110，且a1,a2,a4成等比數(shù)列。(1)證明a1=d

熱心網(wǎng)友

{an}是一個(gè)公差為d（d不等于0）的等差數(shù)列，a1,a2,a4成等比數(shù)列==(a1+d)(a1+d)=a1(a1+3d)==a1^2+2a1d+d^2=a1^2+3a1d==2a1+d=3a1==a1=d

熱心網(wǎng)友

由a1,a2,a4成等比數(shù)列得:a1*a4=a2*a2 == a1(a1+3d)=(a1+d)(a1+d) ==a1=d