tolong jawabkan no.3&4 beserta caranya

Penyelesaian:

3. Sn = 5,050
n = ...? dan Un = ...?

Jawab

Sn = n/2(2a + (n-1)b)
Un = a + (n-1)b

5050 = n/2(2a + (n-1)b)
10100 = n(2a + (n-1)b)
n = 10,100 / (2a + (n-1)b)
n = 10,100 / a + Un   (nilai n)

n = 10,100 / a + Un
an + Un.n = 10100
Un.n = 10100 - an
Un = (10,100 / n) - a  (nilai Un)

4. Sn = 4n²(n+1)
U4 = ...?

Jawab

U4 = S4 - S3
= 4(4)²(4+1) - 4(3)²(3+1)
= 64(5) - 36(4)
= 320 - 144
U4 = 176