A. Maths ( Differentiation)

d/dx (2 開方 x / x-1) = (x+1) / (開方 x (x-1)sqr)

d/dx (2 開方 x / x-1) at (x=4) = 5 / 18

when x = 4, y = 4 /3

Equation of tangent:
y-4/3 = 5/18(x-4)

=> 5x-18y+4=0