If the coefficient of $$x^{12}$$ in the expansion of $$(x^3 + 1)^m$$ is 210, then the coefficient of $$x^{15}$$ is
If m = 10 => $$10_{C_6}\left(x^3\right)^4\left(1\right)^6=\ 210x^{12}$$
Hence $$10_{C_5}\left(x^3\right)^5\left(1\right)^5=\ 252x^{15}$$
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