jumlah semua suku deret aritmatika tersebut adalah....?

dik : ut = 23
un = 43
u3 = 13


[tex]ut = \frac{a + un}{2} \\ 23 = \frac{a + 43}{2} \\ 23 \times 2 = a + 43 \\ 46 = a + 43 \\ a = 46 - 43 \\ a = 3[/tex]

[tex]u3 = a + (3 - 1)b \\ 13 = 3 + 2b \\ 13 - 3 = 2b \\ 10 = 2b \\ b = \frac{10}{2} = 5[/tex]

[tex]un = a + (n - 1)b \\ 43 = 3 + (n - 1)5 \\ 43 = 3 + 5n - 5 \\ 43 = 5n - 2 \\ 43 + 2 = 5n \\ 45 = 5n \\ n = \frac{45}{5} = 9[/tex]


[tex]s9 = \frac{9}{2} (2(3) + (9 - 1)5) \\ s9 = \frac{9}{2} (6 + 40) \\ s9 = \frac{9}{2} \times 46 \\ s9 = 207[/tex]
jawabannya a