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Question 1
28108

Over what domain interval is the function \(y = \dfrac{1}{3}{x^3} + \dfrac{5}{2}{x^2} + 6x - 2\) decreasing ?

\( - 3 < x < - 2\)

\begin{align}
&\begin{aligned}
y &=\frac{1}{3} x^{3}+\frac{5}{2} x^{2}+6 x-2 \\
y^{\prime} &=\frac{1}{3} \times 3 x^{2}+\frac{5}{2} \times 2 x+6 \\
&=x^{2}+5x+6\\
&=(x+3)(x+2)
\end{aligned}\\
&\text{Decreasing when }y^{\prime}<0\\
&\therefore(x+3)(x+2)<0\\
&\text{From the graph}\\
&\therefore-3<x<-2
\end{align}

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