Question

a1=28,8,a6=26,3,an=23,3,n-?

Answer 1

$a_{n}=a_{1}+(n-1)d \ a_{6}=a_{1}+5*d=26.3 \ d= frac{a_{6}-a_{1}}{5}= frac{26.3-28.8}{5}=-0.5 \ a_{n}=28.8+(n-1)*(-0.5)=23.3 \ n=1+ frac{a_{n}-a_{1}}{d}=1+ frac{23.3-28.8}{-0.5}=12$