a.
\(y'=\left(x^2\right)'+\left(4sinx\right)'=2x+4cosx\)
b.
\(y'=\left(2x^3\right)'-\left(sinx\right)'+\left(2\right)'=6x^2-cosx\)
c.
\(y'=\left(5sin\left(x-\dfrac{\pi}{4}\right)\right)'=5cos\left(x-\dfrac{\pi}{4}\right).\left(x-\dfrac{\pi}{4}\right)'=5cos\left(x-\dfrac{\pi}{4}\right)\)