edited by
452 views
0 votes
0 votes

If $x=1+2a+3a^{2}+4a^{2}+\dots(-1 < a < 1)$ and

$y=1+3b+6b^{2}+10b^{3}+\dots(-1 < b < 1),$

then find $1+ab+(ab)^{2}+(ab)^{3}+\dots$ in terms of $x$ and $y$.

  1. $\frac{x^{1/2} y^{1/3}}{x^{1/2}+y^{1/3}-1}$
  2. $\frac{xy}{x+y-1}$
  3. $\frac{x^{1/3}y^{2/3}}{x^{1/3}+y^{1/2}-1}$
  4. None of these.
edited by

Please log in or register to answer this question.

Related questions

0 votes
0 votes
0 answers
2
makhdoom ghaya asked Dec 31, 2015
556 views
There are three coplanar parallel lines. If any $p$ points are taken on each of the lines, then find the maximum number of triangles with the vertices of these points.$p^...
0 votes
0 votes
0 answers
4
makhdoom ghaya asked Dec 31, 2015
553 views
A train crosses a platform $100$ meters long in $60$ seconds at a speed of $45$ km per hour. The time taken by the train to cross an electric pole, is$8$ seconds$1$ minut...