Question

calcule a soma dos 40 termos iniciais da p.a (5,13,21...).​

Answer 1

☑️ Encontrar a razão

• $\small{r=a_{2}-a_{1}}$

• $\small{r=13-5}$

• $\small{r=8}$

☑️ Encontrar o termo a40

• $\small{a_{n}=a_1+(n-1).r}$

• $\small{a_{40}=5+(40-1).8}$

• $\small{a_{40}=5+(49).8}$

• $\small{a_{40}=397}$

☑️ Encontrar a soma ( a40)

• $\small{sn=\dfrac{(a1+a_{n}).n}{2}}$

• $\small{s_{40}=\dfrac{40.(5+397)}{2}}$

• $\small{s_{40}=20.(402)}$

• $\green{\boxed{\small{s_{40}= 8040}}}$

☑️ A soma será portanto 8040