The sum of the series `1/1.2-1/2.3+1/3.4-1/4.5+` ... is

The sum of the series 1/(2!)-1/(3!)+1/(4!)-... upto infinity is (1) e^(-2) (2) e^(-1) (3) e^(-1//2) (4) e^(1//2)

The sum of the series (1)/(1*2)-(1)/(2*3)+(1)/(3*4)--- upto oo is equal to

FInd the sum of infinite terms of the series (1)/(1.2.3)+(1)/(2.3.4)+(1)/(3.4.5)....