Question

Barisan aritmatika dengan u5 = 7 dan u8 = 13 suku ke20?

Answer 1

U5 = a + 4b
7 = a + 4b

U8 = a + 7b
13 = a + 7b

eliminasikan
13 = a + 7b
7 =   a + 4b   -
 6 = 3b
 2 = b

cari a
7 =  a+ 4b
7 = a + 4.2
7 = a + 8
-1 = a

U20 = a + (20-1)b
U20 = -1 + 19.2
U20 = -1 + 38
U20 = 37