y = (1-√x)/(1+√x) = [2-(1+√x)/(1+√x) = 2 - 1/(√(1+x)dy/dx = -1/(1+√x)² *1/(2√x) = - 1/{2√x*(1+√x)²]dy/dx |(x=4) = - 1/{2√4*(1+√4)²] = -1/[2*2*(1+2)²] = -1/36
