# Find sum of first n terms of series : $\;1+\large\frac{1}{1+2}+\large\frac{1}{1+2+3}+\;....$
$(a)\;\large\frac{n}{n-1}\qquad(b)\;\large\frac{2n}{n+1}\qquad(c)\;\large\frac{2n}{n-1}\qquad(d)\;\large\frac{n}{n+1}$