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f\left(x\right)=3x\sin x
a)
f\left(\frac{\pi}{2}\right)=\frac{3\pi}{2}\sin\frac{\pi}{2}=\frac{3\pi}{2}
b)
f'\left(x\right)=3x\cos+3\sin x
f'\left(\frac{\pi}{2}\right)=3
c)
g\left(x\right)=3x