Quotient rule:
f(x) = g(x) / h(x)
f ' (x) = (g'(x) * h(x) - h'(x) * g(x)) / (h(x))^2
g(x) = 5x - 4
g'(x) = 5
h(x) = (5x^2 - 8x + 4)^(1/2)
h'(x) = (1/2)(5x^2 - 8x + 4)^(-1/2)(10x - 8)
h'(x) = (5x - 4)(5x^2 - 8x + 4)^(-1/2)
f ' (x) = ( 5(5x^2 - 8x + 4)^(1/2) - (5x - 4)(5x - 4)(5x^2 - 8x + 4)^(-1/2) ) / (5x^2 - 8x + 4)
f ' (x) = ( 5(5x^2 - 8x + 4)(5x^2 - 8x + 4)^(-1/2) - ((5x - 4)^2)(5x^2 - 8x + 4)^(-1/2) ) / (5x^2 - 8x + 4)
f ' (x) = ( 25x^2 - 40x + 20 - 25x^2 + 40x - 16)(5x^2 - 8x + 4)^(-1/2) / (5x^2 - 8x + 4)
f ' (x) = 4 / (5x^2 - 8x + 4)^(3/2)