120- For which set of values of $a$, the curve $y = x^4 + ax^3 + \dfrac{3}{2}x^2$ is always concave up? (1) $-1 < a < 1$ (2) $-1 < a < 2$ (3) $-2 < a < 1$ (4) $-2 < a < 2$
120- For which set of values of $a$, the curve $y = x^4 + ax^3 + \dfrac{3}{2}x^2$ is always concave up?
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(1) $-1 < a < 1$ \hfill (2) $-1 < a < 2$ \hfill (3) $-2 < a < 1$ \hfill (4) $-2 < a < 2$
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