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a/ \(-1\le sin2x\le1\Rightarrow-7\le y\le-1\)
b/ \(-1\le cos2x\le1\Rightarrow1\le y\le7\)
c/ \(-1\le sin2x\le1\Rightarrow3\le y\le11\)
d/ \(-1\le cos\left(3x+\frac{\pi}{3}\right)\le1\Rightarrow8\le y\le12\)
ADCT: \(\sqrt{u}'=\dfrac{u'}{2\sqrt{u}}\); \(\left(\dfrac{u}{v}\right)'=\dfrac{u'.v-u.v'}{v^2}\)
y'=\(\dfrac{\left(\dfrac{x^3}{x-1}\right)'}{2\sqrt{\dfrac{x^3}{x-1}}}\)
\(\left(\dfrac{x^3}{x-1}\right)'=\dfrac{\left(x^3\right)'.\left(x-1\right)-\left(x-1\right)'.x^3}{\left(x-1\right)^2}\)
=\(\dfrac{3x^2.\left(x-1\right)-x^3}{\left(x-1\right)^2}\)=\(\dfrac{2x^3-3x^2}{\left(x-1\right)^2}\)
=>y'\(\dfrac{2x^3-3x^2}{\left(x-1\right)^2.\sqrt{\dfrac{x^3}{x-1}}}\)=\(\dfrac{2x^3-3x^2}{\sqrt{\left(\dfrac{x}{x-1}\right)^3}}\)
\(y.9=783:3\)
\(\Leftrightarrow9y=261\)
\(\Leftrightarrow y=29\)
Vậy \(y=29\)