Question

Suatu barisan aritmatika dg U2=7 dan U5=19.Nilai U7 adalah.... A.30. B.27. C.24. D.21. pake cara yaaa

Answer 1

U5 = a + 4b = 19
U2 = a +   b =  7   -
              3b = 12
                b = 4

a + b = 7
a + 4 = 7
a = 7 - 4
a = 3

U7 = a + 6b
     = 3 + 6(4)
     = 3 + 24
     = 27...............(B)

Answer 2

U2 =7
a + ( n-1)b = 7
a + (2-1)b =7
a + b = 7 (persamaan 1)

U5 = 19
a + (n-1)b = 19
a + (5-1)b = 19
a + 4b = 19 (persamaan 2) 

eliminasi pers 1 & 2
a + b = 7
a + 4b = 19
-----------------  -- 
      -3b = -12
         b = -12/ -3
         b = 4
subtitusi nilai b k pers 1
a + b = 7
a + 4 = 7
     a = 3
U7 = a + (n-1)b
     = 3 + ( 7-1 ) 4
     = 3 + 6x4
     = 3 + 24
     = 27