Cho \(y=\sin5x\cos2x\). Tính \(y"\left(0\right).\)
\(-5\).\(15\).\(0\).\(-15\).Hướng dẫn giải:\(y=\sin5x\cos2x=\frac{1}{2}\left(\sin3x+\sin7x\right)\Rightarrow y'=\frac{1}{2}\left(3\cos3x+7\cos3x\right)\Rightarrow y"=-\frac{3}{2}\left(3\sin3x+7\sin3x\right)\). Suy ra \(y"\left(0\right)=0.\)