Question

Помогите найти а1 и d

Answer 1

1)  an=3/5*n+2/5
an+1=(3*(n+1)+2)/5=(3n+3+2)/5=(3n+5)/5=3/5*n+1
d=an+1-an=3/5*n+1-3/5*n-2/5=3/5
a1=an-(n-1)*d=3/5*n+2/5-3/5(n-1)=3/5*n+2/5-3/5n+3/5=1

2) an=7/3*n-2/3
an+1=(7*(n+1)-2)/3=(7n+7-2)/3=(7n+5)/3=7/3*n+5/3
d=an+1-an=7/3*n+5/3-7/3*n+2/3=7/3
a1=an-(n-1)*d=7/3*n-2/3-7/3(n-1)=7/3*n-2/3-7/3n+7/3=5/3

3) an=8/5*n+1/5
an+1=(8*(n+1)+1)/5=(8n+8+1)/5=(8n+9)/5=8/5*n+9/5
d=an+1-an=8/5*n+9/5-8/5*n-1/5=8/5
a1=an-(n-1)*d=8/5*n+1/5-8/5(n-1)=8/5*n+1/5-8/5n+8/5=9/5