Question

a soma dos 20 termos de uma pa e 500 se o primeiro termo dessa pa e 5 qual ea razao r dessa pa

Answer 1

$Sn= \dfrac{(a_1+a_n).n}{2} \\\\500= \dfrac{(5+a_n).20}{2} \\\\1000=100+20n\\20a_n=900\\\\\\a_n= \dfrac{900}{20} \\\\\\an=45\\\\\\an=a_1+(n-1).r\\45=5+(20-1).r\\40=19r\\\\\\r= \dfrac{40}{19}$


Forte abraço!