Question

Diketahui deret aritmatika 27+24+21+... jumlah 20 suku pertama deret tersebut adalah

Answer 1

A = 27
b = 24 - 27 = -3

Sn = n/2(2a+(n-1)b)
S20 = 20/2(2.27+(20-1)(-3))
S20 = 10(54+19(-3))
S20 = 10(54+(-57))
S20 = 10(-3)
S20 = -30