MAT 137Y: Calculus with proofs Assignment 6
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MAT 137Y: Calculus with proofs
Assignment 6
Due on Sunday, Feb 19 by 11:59pm via GradeScope
1. (a) Find the area of the bounded region below y = sin x and y = cos x but above the x-axis on [0, π/2].
(b) Find the volume of the solid by rotating the above region about x-axis.
(c) Find the volume of the solid by rotating the above region about y-axis.
(d) Find the volume of the solid by rotating the above region about y = 2. Please set up the integral(s) only. You don’t need to evaluate the integral(s).
(e) Find the volume of the solid by rotating the above region about y = -2. Please set up the integral(s) only. You don’t need to evaluate the integral(s).
(f) Find the volume of the solid by rotating the above region about x = 2. Please set up the integral(s) only. You don’t need to evaluate the integral(s).
(g) Find the volume of the solid by rotating the above region about x = -2. Please set up the integral(s) only. You don’t need to evaluate the integral(s).
2. In this problem, we will prove the Fundamental Theorem of Calculus part 2 by using the definition of the integral.
Theorem 1. Let a, b e R . If f is differentiable on [a, b] and f\ is integrable on [a, b], then
Hint: you may need to use the MVT theorem in your proof.
3. Prove the following theorem:
Theorem 2. Assume a > 0 . Let f be continuous on [0, a] .
Suppose for any 0 < x < 2, we have 0) f (t)dt = xf (x) .
Then there exists c e R such that f (x) = cx on [0, a] .
Hint: Let h(x) = x . What is the derivative of h(x) if f is differentiable on (0, a)?
f (x)
4. Let f be a continuous function on [-π, π] and let m e N be non-zero. Think of f as a complicated wave. Our goal is to approximate it by simpler waves of sine. Let c e R. We want to approximate f (北) by c sin(m北). To choose c optimally, we must quantify the error in this approximation. The quantity
|f (x) - c sin(m北)|
represents the error between the functions at a single point 北 e [-π, π].
Consider
Here, (f (北) - c sin(m北))2 is the square error. The integral represents the average value of the square error on [-π, π].
(a) For c e R, define Fm(c) to be the above integral. Use Fm to find the optimally chosen constant c = cm e R. Give an integral formula for cm .
Hint: Expand the square and write Fm(c) as a quadratic in c. In this question, we treat m as a
fixed positive integer. Also what is sin2 (m北) d北?
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(b) Let’s test your expression for cm . Calculate cm for the function f (x) = x.
(c) Now, let’s try to improve our approximation by comparing f (x) = x to a sum of sine waves. Let N e N be non-zero and c1 , c2 , . . . , cN e R be the fixed optimally chosen constants from (4b). Consider
By expanding the square, find I3 .
(d) Find IN for any non-zero N e N.
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Hint: If m, n e N are both non-zero and m n, what is sin(mx) sin(nx) dx?
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(e) Show that for every non-zero integer N e N that
Remark: Euler spectacularly proved that
You come close to proving this here but a fair bit more is needed to finish it.
2023-02-20