Hitunglah jumlah deret arimetika 3+8+13...+63? Cara nya

3+8+13...+63
u1 = 3
b = 5
Un= 63

Un = u1+(n-1)b
63 = 3+ ( n-1) 5
63-3 = (n-1)×5
60 = (n-1)×5
60/5 =(n-1)
12 =(n-1)
12+1 = n
13 = n

Sn = n/2( u1+un)
= 13/2 ( 3+63)
= 13/2× 66
=13 ×33
=429