Question

Deret aritmatika U6+U9+U12+U15 = 20 tentukan S20

Answer 1

Un= a+(n-1)b maka:

U6= a+(6-1)b = a+5b

U9= a+(9-1)b = a+8b

U12= a+(12-1)b = a+11b

U15= a+(15-1)b = a+14b

U6+U9+U12+U15 = 20

a+5b+a+8b+a+11b+a+14b=20

4a+38b=20

2a+19b=10

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

S20= 20/2(2a+(20-1)b)

S20= 10(2a+19b)

S20= 10(10)

S20=100

Answer 2

Jawaban terlampir....

________________________________

Mapel : Matematika

Materi : Barisan dan Deret

Kode : 9.2.2