Question

a1=2 an=87 Sn=801 d=? n=?

Answer 1

$S_{n}= frac{a_{1}+a_{n}}{2}n \ n=frac{2S_{n}}{a_{1}+a_{n}}=frac{2*801}{2+87}=18 \ a_{n}=a_{1}+(n-1)d \ d= frac{a_{n}-a_{1}}{n-1}=frac{87-2}{18-1}=5$