Let f : R2 → R differentiable with f(a, b) = 5, ∂f/∂x (a, b) ≠ 0 and ∂f/∂y (a, b) ≠ 0. Let C be the intersection curve of the equation f(x, y) = 5 and u→ a nonzero vector tangent to C at the point (a, b).    Detail whether each of the following statements is true or false:   I. ∂f/du→ ≠ 0 necessarily. II. ∇f(a, b)·u→ = 0, necessarily III. If v→ is any vector and w→ = ∇f(a, b), then we necessarily have ∂f/dw→(a,b)≥ df/dv→(a,b).  IV. r(t) = (a + df/dx (a,b) t, b - df/dy (a,b) t), t ∈ R, is the equation of the line normal to C at (a,b).  V. If γ(t) = (x(t), y(t)), t ∈ I, where I is some open interval, is a parametrization of C and h(t) = f(γ(t)), then h'(α) = 0, where α ∈ I is such that γ(α) = (a, b).

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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Let f : R2 → R differentiable with f(a, b) = 5, ∂f/∂x (a, b) ≠ 0 and ∂f/∂y (a, b) ≠ 0. Let C be the intersection curve of the equation f(x, y) = 5 and u a nonzero vector tangent to C at the point (a, b). 

 

Detail whether each of the following statements is true or false:

 

I. ∂f/du ≠ 0 necessarily.

II. ∇f(a, b)·u = 0, necessarily

III. If v is any vector and w = ∇f(a, b), then we necessarily have ∂f/dw(a,b)≥ df/dv(a,b). 

IV. r(t) = (a + df/dx (a,b) t, b - df/dy (a,b) t), t ∈ R, is the equation of the line normal to C at (a,b). 

V. If γ(t) = (x(t), y(t)), t ∈ I, where I is some open interval, is a parametrization of C and h(t) = f(γ(t)), then h'(α) = 0, where α ∈ I is such that γ(α) = (a, b).

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