Question

Pada suatu deret aritmatika diketahui U14 = 57 dan S14 = 434. tentukan selisih antara U3 da U11..???

Answer 1

Sn = n/2 (a+Un)
S14 = 14/2 (a+U14)
434 = 7(a+57)
434 = 7a+399
434-399 = 7a
35 = 7a ----->> a = 5 ----->> U14 = a+13b
57 = 5+13b
57-5 = 13b
52 = 13b ------>> b = 4

U3 = a+2b = 5+2.4 = 5+8 = 13
U11 = a+10b = 5+10.4 = 5+40 =45

jadi,selisihnya = 45-13= 32