Question

Jika U1= sqrt 5 dan U3 = 10 + sqrt 5 berapakah Sn deret geometri tersebut

Answer 1

U1 = √5
u3 = 10+6√5

r² = u3/u1
r² = (10+6√5)/√5
r² = 2√5 + 6
 r = √(6+2√5)
 r = 1 + √5

Sn = a(rⁿ-1)/(r-1)
Sn = √5.((1+√5)ⁿ - 1)/((1 + √5)-1)
Sn = √5.((1+√5)ⁿ - 1)/(√5)
Sn = (1+√5)ⁿ - 1