n=2Sn/(a1+an)=2×888÷(20+54)=24d=(an-a1)/(n-1)=(54-20)÷(24-1)=34/23
sn=(a1+an)/2*n=888(20+54)/2*n=888n=24an=a1+(n-1)d=5420+23d=54d=34/23
n=24.d=34/23
n=24, d=34/23
