1.

निम्न श्रेणियों का योग ज्ञात कीजिए | `x(x+y)+x^(2)(x^(2)+y^(2))+x^(3)(x^(3)+y^(3))`+...n पदों तक

Answer» Correct Answer - `x^(2)((1-x^(2n)))/((1-x^(2)))+xy((1-x^(n)y^(n)))/((1-xy))`
`x(x+y)+x^(2)(x^(2)+y^(2))+x^(3)(x^(3)+y^(3))+….nपदों तक`
`=(x^(2)+xy)+(x^(4)+x^(2)y^(2))+(x^(6)+x^(2)y^(3))+…..पदों तक`
`=(x^(2)+x^(4)+x^(6)+…+nपदों तक)+{xy+(xy)^(2)+(xy)^(3)+….nपदों तक}`
`=S_(1)+S_(2)" "`.....(i)
जहाँ `" "S_(1)=(a(r^(n)-1))/(r-1)=(x^(2){(x^(2))^(n)-1})/(x^(2)-1)=(x^(2)(x^(2n)-1))/(x^(2)-1)`
`S_(2)=(xy{(xy)^(n)-1})/(xy-1)`
समीकरण (i)में `S_(1)`व `S_(2)` का मान रखने पर


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