Question

Qual a quantidade de termos da PA (10,7,..
‚ -20)?

Answer 1

$> \: resolucao \\ \\ \geqslant \: progressao \: \: aritmetica \\ \\ r = a2 - a1 \\ r = 7 - 10 \\ r = - 3 \\ \\ = = = = = = = = = = = = = = = \\ \\ an = a1 + (n - 1)r \\ - 20 = 10 + (n - 1) - 3 \\ - 20 = 10 + ( - 3n) + 3 \\ - 20 = 13 + ( - 3n) \\ - 20 - 13 = - 3n \\ - 33 = - 3n \\ n = \frac{ - 33}{ - 3} \\ n = 11 \\ \\ \\ resposta \: > \: \: pa \: de \: 11 \: termos \: \\ \\ \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \geqslant$

Answer 2

Resposta:

$\textsf{Leia abaixo}$

Explicação passo-a-passo:

$\mathsf{ PA\,(10,7,\dotsc,-20)}$

$\mathsf{a_n=-20;~ a_1=10;~r=-3;~n=\,? }$

$\mathsf{n=\dfrac{a_n-a_1}{r}+1 }$

$\mathsf{n=\dfrac{-20-10}{-3}+1 }$

$\mathsf{n=\dfrac{-30}{-3}+1 }$

$\mathsf{n=10+1 }$

$\boxed{\boxed{\mathsf{n=11}} }$