(5y-3x)·(25y²+15yx+9x²) = 5y·(25y²+15yx+9x²)-3x·(25y²+15yx+9x²) = 125y³+75xy²+45x²y-75xy²-45x²y-27x³ = 125y³-27x³
(5y-3x)·(25y²+15yx+9x²) = 5y·(25y²+15yx+9x²)-3x·(25y²+15yx+9x²) = 125y³+75xy²+45x²y-75xy²-45x²y-27x³ = 125y³-27x³