Let x=1+a +a^(2) +….. And y= 1 + b + b^(...

Let `x=1+a +a^(2) +`….. And `y= 1 + b + b^(2)+`…… where `|a| lt 1` and `|b| lt 1`. Prove that: `1+ ab + a^(2)b^(2) +…… =(xy)/(x+y-1)`.

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