Question

the 7th term of an ap is 40 the sum of its first 13th term is __________________. A)5oo. B)51O. C)52O. D)53O​

Answer 1

Answer:

$7th \: \: term \: \: = a + 6d = 40 \\ \\ sum \: \: of \: \: 13 \: \: terms \: = \frac{13}{2} (2a + 12d) \\ \\ = \frac{13}{2} (2)(a + 6d) = 13(40) = 520$