Question

Diketahui barisan geometri suku ke 3 = 36 dan suku ke 5 = 324. tentukan :
a. suku ke 1 + suku ke 9
b. suku ke 12 + suku ke 20

mohon diisikan rumusnya
#terimakasih

Answer 1

rumus geometri Un = ar^n-1

U3 = ar^3-1

36 = ar^2

36/r^2 = a

U5 = ar^5-1

324 = ar^4

324 = (36/r^2)r^4

324 = 36r^2

324/36 = r^2

√9 = r

3 = r

36/r^2 = a

36/9 = a

4= a

a. U1+U9 = ar^0 + ar^8 = (4x1)+(4x3^8) = 4+26.244 = 26.248

b. U12+U20 = ar^11 + ar^19 = (4x3^11)+(4x^19) = 708.588 + 4.649.045.868 = 4.649.754.456