Tolong bantu saya yang no 2

semoga membantu
terima kasih

e. a = 14
b = 18 - 14 = 4
sn.....?
[tex]sn = \frac{n}{2} (2a + (n - 1)b) \\ = \frac{n}{2} (2(14) + (n - 1)4) \\ = \frac{n}{2} (28 + 4n -4) \\ = \frac{n}{2} (24 + 4n) = \frac{24n + {4n}^{2} }{2} \\ = 12n + {2n}^{2} = n(2n + 12)[/tex]
semoga membantu