Question

Qual a alternativa correta

Answer 1

Resposta:

b) 1040

Explicação passo a passo:

$r=a_{2}-a_{1}\\r=86-90\\r=-4$

$a_{n} = a_{1}+(n-1).r\\a_{20} = 90+(20-1).(-4)\\a_{20} = 90+(19).(-4)\\a_{20} = 90+(-76)\\a_{20} = 90-76\\a_{20} = 14$

$S=\frac{(a_{1}+a_{n}).n}{2} \\\\S=\frac{(90+14).20}{2} \\\\S=\frac{(104).20}{2} \\\\S=\frac{2080}{2} \\\\S=1040$

Answer 2

Resposta:

b) 1040 e a resposta correta