Answer:
\left(\frac{x}\sqrt\left-\frac{\sin \left(x\right)\cos \left(400x\right)}{2\sqrt{\cos \left(x\right)}}-400\sin \left(400x\right)\sqrt{\cos \left(x\right)}\right)\left(4-x^{1.1}\right)+\left(-1.1x^{0.1}\right)\left(\cos \left(400x\right)\sqrt{\cos \left(x\right)}+\sqrtx\right-0.4\right)
Explanation:
\frac{d}{dx}\left(\left(\sqrt{\cos \left(x\right)}\cos \left(400x\right)+\sqrt\left-0.4\right)\left(4-xx^{0.1}\right)\right)
=\left(\cos \left(400x\right)\sqrt{\cos \left(x\right)}+\sqrt\left-0.4\right)\left(4-x^{1.1}\right)
=\frac{d}{dx}\left(\cos \left(400x\right)\sqrt{\cos \left(x\right)}+\sqrt\left-0.4\right)\left(4-x^{1.1}\right)+\frac{d}{dx}\left(4-x^{1.1}\right)\left(\cos \left(400x\right)\sqrt{\cos \left(x\right)}+\sqrt\left-0.4\right)
=\frac{x}\sqrtx\right-\frac{\sin \left(x\right)\cos \left(400x\right)}{2\sqrt{\cos \left(x\right)}}-400\sin \left(400x\right)\sqrt{\cos \left(x\right)}