等差数列{an}的首项为a，公差为d；等差数列{bn}的首项为b，公差为e。如果cn=an+bn（n>=1)且c1=4,c2=8,

c1=a1+b1=4 c2=a2+b2=(a1+d)+(b1+e)=8 ==> d+e=4 an=a1+(n-1)d bn=b1+(n-1)e cn=an+bn=(a1+b1)+[(n-1)d+(n-1)e] =4+(n-1)(d+e) =4+4(n-1) =4n