Find the coefficient of $x^5$ in the expression $(5x+12x^2+15x^3+8x^4)^{15}$
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Apply multinomial expansion and group terms. – Sunyam Oct 21 '17 at 06:36
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Notice that the polynomial with the lowest degree is $5x$, which has a degree of $1$. Since this is multiplied by itself $15$ times, does a coefficient of $x^5$ even exist?
Toby Mak
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