by Unszorgné Markó Andrea 3 years ago
204
More like this
by Szücs Vivien
by Ecsedi Margareta
Sn=( a1+an)/2*n=( 2a1+(n-1)d)*n
an= a1+(n-1)∙˙d
Sn=a1*(qn-1)/(q-1)
an= a1*qn-1