7.
f'(x) = 5 - 9/x²
f'(3/4) = 5 - 9/(9/16) = 5 - 16 = -11
9.
f(x) = (x-4)/((x-4)(x+4)) = 1/(x+4), x ≠ 4
f'(x) = -1/(x+4)²
f'(-4,5) = -1/(-0,5)² = -1/0,25 = -4
11.
f'(x) = 9/√x
f'(9) = 9/√9 = 9/3 = 3
12.
f'(x) = 4/2 * 1/√(4x-7) = 2/√(4x-7)
f'(2) = 2/√(8-7) = 2