举报
峰峰8218
d=0.5 a1+a3+a5+...+a99 =a1+(a1+2*d+a1+4*d+...+(a1+98*d)=60///1+98/2=50 50*a1+(2+4+6+...+98)*d=50*a1+2450*d=60 a1 a1+a2+a4+...+a100 =a1+(a1+d)+(a1+3*d)+...+(a1+99*d)///1+99+1/2=51 =51*a1+(1+3+..+99)*d =51*a1+2500d Ҫǵڶûa1,Կ a1+a3+a5+...+a99=60 a2+a4+a6+...+a100=s ʽ 50*d=s-60 s=60+50*d ǵa1 s1=s+a1