Question

Calcule a soma da pa sabendo que a15=95 e a razão r = 7​

Answer 1

Resposta:

$\textsf{Leia abaixo}$

Explicação passo a passo:

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

$\mathsf{95 = a_1 + (15 - 1)7}$

$\mathsf{95 = a_1 + (14)7}$

$\mathsf{95 = a_1 + 98}$

$\mathsf{a_1 = 95 - 98}$

$\mathsf{a_1 = -3}$

$\mathsf{S_n = \dfrac{(a_1 + a_n)n}{2}}$

$\mathsf{S_{15} = \dfrac{(95 - 3)15}{2}}$

$\mathsf{S_{15} = \dfrac{(92)15}{2}}$

$\mathsf{S_{15} = \dfrac{1.380}{2}}$

$\boxed{\boxed{\mathsf{S_{15} = 690}}}$

Answer 2

Resposta:

sn=690

Explicação passo-a-passo:

an=a1+(n-1)•r

an =95

r=7

n=15

a1=?

95=a1+(15-1).7

95=a1+14•7

95=a1+98

95-98=a1

a1= -3

$sn = \frac{(a1 + an).n}{2}$

$sn = \frac{( - 3 + 95).15}{2} = \frac{92.15}{2} = \frac{1380}{2} = 690$