Question

Calcular el número de términos, dados:
a) a1 = 13; d = 10; an = 133.
b) a1 = 14; an = 120; S = 1005.

Answer 1

Respuesta:

a) a1 = 13; d = 10; an = 133.

an = a1+(n-1)d

an = 13+(n-1)10

an = 13+10n-10

an = 10n+3

10n+3 = 133

10n = 133-3

10n = 130

n = 130/10

n = 13

Son 13 términos

b) a1 = 14; an = 120; S = 1005.

Sn = (a1+an)n/2

(14+120)n/2 = 1005

(134)n/2 = 1005

134n = 1005*2

134n = 2010

n = 2010/134

n = 15

Son 15 términos