Question

Diketahui suatu barisan aritmatikadengan U5=7 dan U8=13. suku ke-20 adalah..
a.39
b.37
c.-37
d.-39

Answer 1

U8 = a + 7b = 13
u5 = a + 4b = 7
________________-
3b = 6
b = 2

u5 = a + 4b = 7
a + 4.2 = 7
a = -1

Jd
u20 = a + 19b
-1 + 19.2 = 37

Answer 2

U5 = a + 4b = 7
u8 = a + 7b = 13 -
          - 3b = -6

b = -6/-3 = 2

a + 4b = 7
a + 4(2) = 7
a = 7-8
a= -1

u20 = a + 19b
     = -1 +19(2)
     = -1 + 38
   = 37