Question

1.2 + 2.3 + 3.4 + 4.5 + . . . + 2013.2014 = ????

Answer 1

Temos a formula do PA = $\frac{(a1 + an)n}{2}$

então:
a1 = 1.2 
an = 2013.2014
n = 2013 (olha a sequencia do 1,... 2,..., 3,...... )

$\frac{(1.2 + 2013.2014)*2013}{2}$  = 2027495,0091