Question

20,42,66,92,120 rumus suku ke n

Answer 1

Deret aritmatika bertingkat
a = 20
b = 22
c = 2

un = a+(n-1)b+(n-1)(n-2)c/2
un = 20+(n-1)22+(n-1)(n-2)2/2
un = 20+22n-22+n²-3n+2
un = n²+19n

Answer 2

Ni = sigma [20+(2xi)]i

i = 0,1,2,3,4,5....