suku pertama barisan aritmatika adalah 36 sedangkan suku ke 12 = 30 tentukan suku ke 7

Un = a + ( n - 1 ) b

U1 = a = 36

U12 = a + 11b
30 = 36 + 11b
11b = 30 - 36
b = - 6/11

U7 = a + 6b
= 36 + 6(-6/11)
= 36 - 36/11
= 36 - 3 3/11
= 32 8/11

U1 = a = 36
Jika a = 36 maka b adalah
U12 = a + 11b = 30
          36 + 11b = 30
                  11b = 30 - 36
                     b = -6/11
U7 = a + 6b = 36 + 6(-6/11)
                    = 36 + -36/11
                    = 396/11 - 36/11
                    = 360/11

Insya Allah benar