the coefficient of x2 inthe expansion of (1+9x+27x^2+27x^3)^10

Dear sri

(1+9x+27x²+27x³)¹⁰

 = (1+3x)³⁰

so co efficient of x² is = ³⁰C₂ 3²

                                        =9³⁰C₂

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