Question

Diketahui U1=5 dan U5= -3 tentukan jumlah 20 suku pertamanya!


#dengan caranya

Answer 1

U1 = a = 5
U5 = a + 4b
-3 = 5 + 4b
4b = - 5 - 3
b = -8/4
b = -2

S20 = 20/2 x (2a + 19b)
S20 = 10 x (10 - 38)
S20 = 10 x (-28)
S20 = - 280