y = (1-x)/(1+x)= [2-(1+x)]/(1+x) = 2/(1+x) - 1
dy/dx = -2/(1+x)²
d²y/dx² = -2²/(1+x)³
d³y/dx³ = 3×2²/(1+x)⁴
.
dⁿy/dxⁿ = (-1)ⁿ×2×n!/(1+x)ⁿ+¹