Question

encontar o vigésimo termo do P.A ( 2,7,12,17)... e a soma desses termos

Answer 1

$a_n = a_1+(n-1)*r\\\\ a_2_0 = 2+(19)*5\\\\ a_2_0 = 2+95\\\\ \boxed{a_2_0 = 97}$

$S_n = \frac{(a_1+a_n)*n}{2}\\\\ S_2_0 = \frac{(2+97)*20}{2}\\\\ S_2_0 = \frac{99*20}{2}\\\\ \boxed{S_2_0 = 990}$