diketahui barisan : 7, 11, 15, 19, 23, . suku ke berapakah yang nilainya 431 ?

Barisan Aritmatika

7, 11, 15, 19, ...
a = 7
b = 11 - 7 = 4

Un = a + (n - 1)b
Un = 7 + 4(n - 1)
Un = 4n + 3

431 = 4n + 3
4n = 428
n = 428/4
n = 107

431 = U107 ✓