1. Diketahui barisan aritmatika dengan U1= 3, Un= 87, dan U6 + U7 = 9. Tentukan : a) b=...? b) n=...? c) U50=....?

Pake caraa .. please jawab yaaa:)

1. Diketahui barisan aritmatika dengan U1= 3, Un= 87, dan U6 + U7 = 9. Tentukan : a) b=…? b) n=…? c) U50=….?

U1 = a = 3

U6 + U7 = 9
[a + (6-1)b] + [a + (7-1)b] = 9
[3 + 5b] + [3 + 6b] = 9
6 + 11b = 9
11 b = 9 – 6
11b = 3
b = $frac{11}{3}$

Un= 87
a + (n-1)b = 87
3 + (n-1) $frac{11}{3}$ = 87
3 + $frac{3}{11} n$ – $frac{3}{11}$ = 87
$frac{36}{11}$ + $frac{3}{11} n$ = 87
$frac{3}{11} n$ = 87 – $frac{36}{11}$
$frac{3}{11} n$ = $frac{957}{11}$
3n = 957
n = 319

U50 = 3 + 49b
       = 3 + 49 $frac{3}{11}$
   = 3 + 13,3
   = 16,3

semoga membantu 🙂