※ 引述《faithinu (彩色的肝)》之銘言：
: 方法一沒問題
: 請問方法二畫底線部分的那個根號怎麼來的？
: https://i.imgur.com/BCghDAE.jpg
f(x, y, z) = z - g(x, y)
n = ▽f / |▽f|
= ([email protected]/@x, [email protected]/@y, 1) / √[([email protected]/@x)^2 + ([email protected]/@y)^2 + 1]
ndA * k = dxdy
=> dA = √[([email protected]/@x)^2 + ([email protected]/@y)^2 + 1] dxdy