Question

Qual é o numero de termos da PA em que An=-186,A1=1 e r=-11?​

Answer 1

$\mathsf{a_{n}=a_{1}+(n-1).r} \\ \mathsf{\to~n=\dfrac{a_{n}-a_{1}}{r}+1}$

$\mathsf{n=\dfrac{-186-1}{-11}+1}\\\mathsf{n=\dfrac{-187}{-11}+1}\\\mathsf{n=17+1}$

$\huge\boxed{\boxed{\boxed{\boxed{\mathsf{n=18}}}}}$

Answer 2

resolução!

an = a1 + ( n - 1 ) r

- 186 = 1 + ( n - 1 ) - 11

- 186 = 1 + ( - 11n ) + 11

- 186 = 12 + ( - 11n )

- 186 - 12 = - 11n

- 198 = - 11n

n = 198 / 11

n = 18

resposta: PA de 18 termos