Work Step by Step
$3x^3\lt-15x^2\\3x^3+15x^2\lt0\\3x^2(x+5)\lt0$ We know that $(x-k)^2\geq0$ for all $k$. So here for the inequality to be true, $x+5\lt0\\x\lt-5$ So the solution is $x\lt-5$
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