Question

Determine a somo dos trinta primeiros termos da P.A (-4,-2, 0, 2, 4, 6,...)

Answer 1

$P.A(-4,-2,0,2,4,6)\\\\r=a2-a1\\r=-2-(-4)\\r=-2+4\\r=2\\\\Como\,\,r\ \textgreater \ 0, temos\,uma\,P.A\,crescente\\\\n=30\\an=?\\\\a_n=a_1+(n-1).r\\a_{30}=-4+(30-1).2\\a_30=-4+58\\a30=54\\\\Soma\,dos\,30\,primeiros\,termos\,dessa\,P.A\\\\S_n=\dfrac{(a_1+a_n).n}{2}\\\\S_n=\dfrac{(-4+54).30}{2}\\\\S_n=50.15\\\\S_n=750$

Answer 2

-4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54
Lembrando que são os trinta primeiros e não até trinta.

Sn=(a1+an).n S30=(-4+54).30 S30=50.30
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2 2 2

S30=1,500. S30= 750
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