Diketahui suatu barisan aritmatika dengan U2=7 dan U6=19,tentukan suku ke 41

jawab

u2  = 7
u6  =19

u6 - u2 = 19 - 7
(6-2)b = = 12
4b = 12
b = 3

u41 = a + 40 b
= a + 5b + 35 b
= (a + 5b) + 35b
= u6 + 35(3)
= 19 + 105
= 124

dik : U2 = 7    > a + (n-1)b = 7   > a + (2-1)b =7    > a + 1b = 7
        U6 = 19  > a + (n-1)b = 19 > a + (6-1)b = 19 > a + 5b = 19

Dit : U41=... ?

penye : #eliminasi                                 #subtitusi
              U6 => a + 5b =19                       a + 1b = 7
              U2 => a + 1b =  7                       a +1(3)= 7
                               4b = 12                      a + 3   = 7
                                 b = 3                        a        = 7-3
                                                                 a        = 4

           U41 = a + (n-1)b
                   = 4 + (41-1)3
                   = 4 +  40.3
                   = 4 + 120
                   =124