Question

quantos termos tem a PA finita (-2,3...43)

Answer 1

a1 = -2
a2 = 3
r = 3 - ( -2) = 3 + 2 = 5 *****
an = 43
an = a1 + (n-1)r
43 = -2 + ( n - 1)5
-2 + 5n - 5 = 43
5n - 7 = 43
5n = 43 + 7
5n = 50
n = 10 ****

Answer 2

Razão  =  a2 - a1
r = 3 - (-2)
r = 5
an = 43
a1 = -2

===

an = a1 + ( n -1) . r
43 = -2 + (  n  -1) . 5
43 = -2 + 5n - 5
43 = -7 + 5n
50 = 5n  
n = 50/5
n = 10