hallo semua tolong di bantu yaa... say..

u5= 3(5)² - 5
= 3(25) - 5
= 75 - 5 = 70

Sn = 3n^2 - n

S1 = 3(1^2) - 1
S1 = 3(1) - 1
S1 = 3 - 1
S1 = 2

S2 = 3(2^2) - 2
S2 = 3(4) - 2
S2 = 12 - 2
S2 = 10

a = S1 = 2

U2 = S2 - S1
a + b = 10 - 2
2 + b = 8
b = 8 - 2
b = 6


Besar suku ke-5 :

Un = a + (n - 1) × b
U5 = 2 + (5 - 1) × 6
U5 = 2 + 4 × 6
U5 = 2 + 24
U5 = 26

Jadi besar suku ke-5 deret tersebut adalah 26