5. (10 分）試求函數f(x) = ln(l + x)之秦勒展開式（Taylor Expansion),在 x=0. (即 Maclaurin Scries )

(c) Assume that f(x,y, z) attains the maximum value at (x, y, z) = (0,1,2) when restricted to a level surface h(x, y, z) = 1, where h(x,y, z) is differentiable and(0, 1,2) = 6. Using linear approximation, estimate the maximum value of f(x, y, z) subject to the nearby level surface h(x,y, 2) = 0.9. The estimated value is approximately (10)