Question

Uma PA de razão 5, o primeiro termo é 6. que lugar ocupa o termo cujo valor é 56?

Answer 1

$r=5\\ a_1=6\\ a_n=56\\n=?\\\\\\ a_n=a_1+(n-1)\times r\\\\\\ 56=6+(n-1)\times 5\to\\\\ 56=6+5n- 5\to\\\\56-6+5=5n\to\\\\ 55=5n\to\\\\ \dfrac{55}{5} =n\to\\\\ \boxed{n=11}\\\\\\\\ PA~\{~6, 11, 16, 21, 26, 31, 36, 41, 46, 51, 56~\}$