Question

Em uma P.A onde a1 = -4 e a20 = 34. Determine a soma dos 20 primeiros termos
1 ponto
A) 280
B) 300
C) 350
D) 380
E) 400
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Answer 1

Explicação passo-a-passo:

$sn = \frac{(a1 + an) \: . \: n}{2} \\ </strong><strong>s_</strong><strong>{20} = \frac{( - 4 \: + \: 34) \: . \: 20}{2} \\ </strong><strong>s_</strong><strong>{20} = \frac{30 \: . \: 20}{2} \\ </strong><strong>s_</strong><strong>{20} = \frac{600}{2} \\ \red{</strong><strong>\</strong><strong>r</strong><strong>m</strong><strong>~</strong><strong>~</strong><strong>~</strong><strong>{</strong><strong> \boxed{</strong><strong>\</strong><strong>b</strong><strong>o</strong><strong>x</strong><strong>e</strong><strong>d</strong><strong>{</strong><strong>s_</strong><strong>{20} </strong><strong>=</strong><strong>300</strong><strong>}</strong><strong>}</strong><strong>}</strong><strong>}</strong><strong>$

espero ter ajudado :)