Tentukan rumus suku n (un) dan besar suku ke 80 barisan bilangan… B. 15, 13, 11, 9….. D. 2/3, 5/7, 8/11, 11/15…

B. 15, 13, 11, 9…..
Un = (13-15)n + 15 – ( 13-15 )
Un = -2n + 15 + 2
Un = 17 – 2n
U80 = 17 – 2×80 = -(160-17) = -153

D. 2/3, 5/7, 8/11, 11/15…
Un = (3n-1)/(4n-1)
U80 = (3×80 -1)/(4×80 -1) = 239/319