tolong bantuannya no 8 ...... beserta cara mengerjakanya....

[tex]a = 28 \\ b = 4 \\ un = 148 \\ \\ un = a + (n - 1)b \\ 148 = 28 + (n - 1)4 \\ 148 = 28 + 4n - 4 \\ 148 = 4n + 24 \\ n = \frac{148 - 24}{4} \\ n = 31 \\ \\ sn = \frac{n}{2} (2a + (n - 1)b \\ s31 = \frac{31}{2} (2(28) + (31 - 1)4) \\ = \frac{31}{2} (56 + 120) \\ = \frac{31}{2} \times 176 \\ = 2728[/tex]