Find the differential dy and evaluate dy for the given values of x and dx:
a) f(x) = cube root of (3x2 - 2) , x = 1, dx = 0.05
b) f(x) = natural log of (cos(x2) ) , x = square root of pi divided by 2, dx = -0.1
c) f(x) = (x2 - 4) divided by (2x) , x = 2, dx = 0