Created by Andi Suparjo, S.Pd., Gr 51 Jawab: a = .... r = .... n = .... U10 = ar..... = .... x ....... = ... x ......... = ........... 2. Tentukan jumlah n suku yang diminta pada setiap barisan geometri berikut: a. 5 + 15 + 45 + .... + 3645 Jawab: a = .... r = .... Un = 3645 arn-1 = 3645 ..... x ....n-1 = 3645 .... n-1 = 3645 / .... = ........ = 3.... n – 1 = .... n = ..... 5 + 15 + 45 + .... + 3645 = S...... S..... = ….(3 ….−1) 3−1 = …..(……….−1) …. = ….…….. …. = … … … … b. 4 + 8 + 16 + ... + 128 a = .... r = ..... Un = 128 arn-1 = 128 .... x ....n-1 = 128 .... n-1 = 128 /.... = ....... = 2.... n – 1 = .... n = .... 4 + 8 + 16 + ... + 128 = S....... S..... = ….(2 ….−1) 2−1 = …..(……….−1) …. = ….…….. …. = … … … … 3. Diketahui suatu barisan geometri dengan a = 1 dan U7 = 64. Tentukan U10 ? Jawab: a = ... U7 = 64 ar..... = 64 ....r..... = 64 r ..... = 64 r = .... U10 = ar..... = 1 (.....).... = .................. 4. Diketahui barisan geometri dengan suku ketiga 27 dan suku kelima 3. Rasionya bilangan positif. Tentukan S6 Jawab:
Created by Andi Suparjo, S.Pd., Gr 52 U3 = 27 U5 = 3 ar..... = 27 ar..... = 3 5 3 = ….. ….. Substitusi r = ...., misalnya ke U3 = ar..... = 27 3 27 = r ...... sehingga didapatkan a = ..... 1 ….. = r ...... r = ....... S6 = (1 − ….. ) 1− = …….(1 − (…….) ….. ) 1− ……… = …….(1 − ……….. ) …………… = .....................................................................................