MAT237 Multivariable Calculus with Proofs Problem Set 1 2022
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MAT237 Multivariable Calculus with Proofs
Problem Set 1
2022
Problems
1. Let a, b ∈ R with a < b and γ : [a, b] → R2 be a differentiable parametric curve. Determine which of the following statements are true or false. If false, give a counterexample. If true, briefly explain why.
(1a) Suppose ∥γ′ (t)∥ > 0 for all t ∈ (a, b) and that ∥γ′ (t)∥ is not constant. Then N(t) and γ′′ (t) are not parallel.
(1b) Suppose [a, b] = [0,6]. If γ(t) is the position of a particle at t seconds, then ∥γ(4)−γ(2)∥ is the distance
the particle travels between 2 and 4 seconds.
2. For each of the sets S ⊆ R3 below, express S in rectangular, cylindrical, and spherical coordinates. (2a) S is the portion of the first octant [0,∞)3 which lay below the plane x + 2y + 3z = 1
(2b) S is the portion of the ball {(x , y, z) ∈ R3 : x 2 + y2 + z2 ≤ 4} which lay below the cone {(x , y, z) ∈ R3 : z = px2 + y2 }
3. Level sets can be very strange. Let A be the circle of radius 2 centered at the origin and let B = {(x , y) ∈ R2 : y = x 2 }. Construct a polynomial f : R2 → R whose π-level set is A∪ B and prove that A∪ B is its π-level set,
4. Let S = {(x , y) ∈ R2 : x + y < 1} and let p = (0.5,0.5).
(4a) Sketch a “picture proof” that p is a boundary point of S . Label your diagram with quantities that would be used in a direct proof by definition. Do not write a full proof.
(4b) Prove from definition that p is a boundary point of S .
5. Prove or provide a counter-example for each of the following statements:
(5a) For any S ⊂ Rn , ∂ S = ∂ SC
(5b) For any S ⊂ Rn , (S )o = So
(5c) For any S ⊂ Rn , (So )o = So
6. For each of the following, find the interior, boundary and closure of each set. Is the set open, closed or neither?
(6a) {(x , y) : 0 < y < x − x2 }
(6b) {(x , y) : x 2 + y2 ≤ 1} \ {(x,0) : 0 < x}
(6c) {(x , ) : x ∈ n, ∈ + }
(6d) ([0,1] ∩ Q)2
2022-05-19