参数方程弧长和表面积
斜边长度平方 (hypotenuse)
(ΔS)2=(Δx)2+(Δy)2(\Delta S)^2 = (\Delta x)^2 +(\Delta y)^2(ΔS)2=(Δx)2+(Δy)2
(dS)2=(dx)2+(dy)2(dS)^2 = (d x)^2 +(d y)^2(dS)2=(dx)2+(dy)2
simplify: dS2=dx2+dy2dS^2 = d x^2 +d y^2dS2=dx2+dy2
ds=1+(dy/dx)2dxds = \sqrt
