Question

O oitavo termo dada a PA(3,5,7,9...) calcule:
A20= S20=

Answer 1

PA(3,5,7,9...)

O 8º=A1+7r =3+7*2=3+14=17 (8º termo)

A20=A1+19r=3+19*2=3+38=41 (20º termo)

S20=$\dfrac{(a1+a20)\times 20}{2}=\dfrac{(3+41)\times 10}{1}=44\times 10=440 (S20)$

Espero ter ajudado