a_n - a_k
d = ---------
n - k
d=−k+n−ak+an a1=an+d(n−1) (-1 + n)*(a_n - a_k)
a_1 = a_n - --------------------
n - k
a1=an−−k+n(−ak+an)(n−1) a_15 - a_6
d = ----------
9
d=9a15−a6 a_15 - a_6
a_1 = a_15 - ----------*13
9
a1=a15−9a15−a6⋅13 182/5 - 35/2
d = ------------
9
d=9−235+5182 182 182/5 - 35/2
a_1 = --- - ------------*14
5 9
a1=(−1)9−235+5182⋅14+5182 d=1021