WAEC - Further Mathematics (2014 - No. 30)
The first term of a linear sequence is 9 and the common difference is 7. If the nth term is 380, find the value of n.
45
54
56
65
Giải thích
\(T_{n} = a + (n - 1)d\)
\(380 = 9 + (n - 1)7\)
\(380 = 9 + 7n - 7 \implies 380 = 2 + 7n\)
\(7n = 380 - 2 = 378 \therefore n = \frac{378}{7} = 54\)