Tolong kak pliss buat besok

Jawab:

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

S12 = 12/2 (2.80 + (12-1)15)

S12= 6 (160 + 165)

S12 = 1.950

Un = a + ( n-1 ) × b

U12 = 80 + (12-1) × 15

= 80 + 11×15

= 80 + 165

= 245