tolong kk jawab soal no 1 dan 2

1. Sighma
.
10
∑    (5k +5) = ..
k =1

k =(1,2,3,...,10)
10+ 15+ 20+ ...+ 55
a=10
b = 5
un = 55 --> 5n+ 5 = 55
5n = 50
n = 10
Sn = n/2 (a + un)
s10 = 10/2(10+ 55) = 5 x65 = 325

2. Artimetika

U10= 41
u5 = 21
u10-  u 5 =  41 - 21
(10-5) b = 20
5b = 20
b = 4

u 5 = 21
a + 4b = 21
a + 4(4) = 21
a =21-16
a  = 5

suku pertama 5  dan beda 4