a.
Do \(-1\le sin3x\le1\Rightarrow-4\le sin3x-3\le-2\)
\(y_{max}=-2\) khi \(sin3x=1\)
\(y_{min}=-4\) khi \(sin3x=-1\)
b.
Do \(-1\le cos2x\le1\Rightarrow0\le cos2x+1\le2\)
\(y_{max}=2\) khi \(cos2x=1\)
\(y_{min}=0\) khi \(cos2x=-1\)
c.
\(y=sin2x.cos2x+2=\dfrac{1}{2}sin4x+2\)
Do \(-1\le sin4x\le1\Rightarrow\dfrac{3}{2}\le\dfrac{1}{2}sin4x+2\le\dfrac{5}{2}\)
\(y_{max}=\dfrac{5}{2}\) khi \(sin4x=1\)
\(y_{max}=\dfrac{3}{2}\) khi \(sin4x=-1\)
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