1.

`(1+3x+3x^(2)+x^(3))^(15)` के विस्तार में `x^(9)` का गुणांक निकालिए |

Answer» `(1+3x+3x^(2)+x^(3))^(15)=[(1+x)^(3)]^(15)=(1+x)^(45)`
`:." ""co-efficient of "x^(9)" in "(1+3x+3x^(2)+x^(3))^(15)`
`="co-eff. of "x^(9)" in "(1+x)^(45)`
`=""^(45)C_(9)" "[because(1+x)^(n)" के विस्तार में "x^(r)" का गुणांक "=""^(n)C_(r)]`
`=(45!)/(9!36!)`


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