If f(x) is meant to equal 3x7 − 4x-2 + 4(3x0.5 + 1),
then f'(x) is constructed as 7(3x7-1) − -2(4x-2-1) + 4[0.5(3x0.5-1)+ d(1)/dx].
This last "cleans up" to yield f'(x) as 21x6 + 8x-3 + 6x-0.5 + 0.
Now go from f'(x) to f''(x).
Write 21x6 + 8x-3 + 6x-0.5 + 0 and differentiate to
6(21x6-1) + -3(8x-3-1) + -0.5(6x-0.5-1).
Reduce this last to gain f''(x) as 126x5 − 24x-4 − 3x-1.5.