Question

achar a soma dos 50 primeiros termos da P.A (2,6...)

Answer 1

S = (a1 + an)*n/2
an = a1 + ( n - 1 )*r
----
a50 = 2 + (50-1)*4
a50 = 2+196
a50 =198

S = (2+198)*50/2
S = (200*50)/2
S = 100*50
S= 5.000

Bons estudos ^_^

Answer 2

P.A.(2,6,......)
A 1 = 2
A 2 = 6
R = A 2 - A 1
R = 6 - 2
R = 4

A 50 = A 1 + (N - 1 )R
A 50 = 2 + (50 - 1 ),4
A 50 = 2 + 49 . 4
A 50 = 2 + 196
A 50 = 198

S n = n . (a 1 + a n) / 2
S 50 = 50.(2 + 198) / 2
S 50 = 50 . 200 /2
S 50 = 10000/2
S 50 = 5000