Question

quantos termos tem a PA (5,10,..., 785) ?

Answer 1

$PA~\{5, 10,..., 785\}\\\\ a_1=5\\ a_n=785\\ r=10-5 = 5\\n=?\\\\\\ a_n=a_1+(n-1)\times r \\\\\\ 785=5+(n-1)\times 5\to\\\\ 785=5+5n- 5\to\\\\785-5+5=5n\to\\\\ 785=5n\to\\\\ \dfrac{785}{5}=n\to\\\\ \boxed{n=157}$

Answer 2

Bom Dia!

Dados:

a1 → 5

an → 785

r → a2-a1 → 10-5 = 5

n → ?

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An=a1+(n-1)·r

785=5+(n-1)·5

785=5+5n-5

785-5n=5-5

-5n=0-785

-5n=-785 (-1)

5n=785

n=785/5

n=157

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Att;Guilherme Lima