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MIT 18.01 Practice Exam 2B

Practice exam for Unit II: extrema and concavity, volume optimization, substitution, related rates and the mean value theorem.

1. MIT 18.01 Practice Exam 2B — how this assessment works

This lesson reproduces the Practice Exam “MIT 18.01 Practice Exam 2B” from MIT OpenCourseWare 18.01 Single Variable Calculus (Fall 2006) (https://ocw.mit.edu/courses/18-01-single-variable-calculus-fall-2006/), licensed under CC BY-NC-SA 4.0. Work through 6 problems in order: type your reasoning in the answer box or write it on the handwriting pad, then submit for AI grading.

How the grading works Every problem is graded by an AI mathematics teacher that reads the official solution shipped with the course. It checks your work criterion by criterion, awards partial credit for correct steps, and returns written feedback. Equivalent mathematics and valid alternative methods are accepted — a different route to the same result can still earn full marks.

If your answer is incomplete, the feedback names exactly which steps are missing, so you can correct them and try again.

2. MIT 18.01 PE2B Problem 1 — Extrema, concavity and sketch of a cubic (20 pts)

Find the local maxima and minima and points of inflection of

2x3+3x2−12x+1.2x^{3}+3x^{2}-12x+1.

Then use this data to sketch its graph on the given axes, showing also where it is convex (concave up) or concave (down). (Note that different scales are used on the two axes.)

3. MIT 18.01 PE2B Problem 2 — Least metal for a popcorn can (20 pts)

A new junk food — NoKarb PopKorn — is to be sold in large cylindrical metal cans with a removable plastic lid instead of a metal top. The metal side and bottom will be of uniform thickness, and the volume is fixed to be 64π64\pi cubic inches.

What base radius rr and height hh for the can will require the least amount of metal?

Show work, and include an argument to show your values for rr and hh really give a minimum.

4. MIT 18.01 PE2B Problem 3 — Three indefinite integrals by substitution (15 pts)

Evaluate the following indefinite integrals:

a)

∫e−3x dx\int e^{-3x}\,dx

b)

∫cos⁡2xsin⁡x dx\int \cos^{2}x\sin x\,dx

c)

∫x dx1−x2\int \frac{x\,dx}{\sqrt{1-x^{2}}}

5. MIT 18.01 PE2B Problem 4 — The escaping prisoner and the searchlight (15 pts)

A searchlight LL is 100 meters from a prison wall. It is rotating at a constant rate of one revolution every 8 minutes. (How many radians/minute is that?)

Martha, an escaping prisoner, is running along the wall trying to keep just ahead of the beam of light.

At the moment when the searchlight angle θ\theta is 60 degrees, how fast does she have to run?

6. MIT 18.01 PE2B Problem 5 — Linear approximation, and a separable differential equation (15 pts: 5 + 10)

a) What value for the constant cc will make the function e−x1+cxe^{-x}\sqrt{1+cx} approximately constant, for values of xx near 00? (Show work.)

b) Find the solution x(t)x(t) to the differential equation

dxdt=2t1−x2\frac{dx}{dt}=2t\sqrt{1-x^{2}}

which also satisfies the condition x(0)=1x(0)=1.

7. MIT 18.01 PE2B Problem 6 — Two applications of the Mean-value Theorem (15 pts: 8 + 7)

a) Use the Mean-value Theorem to show that ln⁡(1+x)<x\ln(1+x)<x, if x>0x>0.

(You do not have to state the theorem.)

b) Let cc be any constant. Show that the function f(x)=x3+x+cf(x)=x^{3}+x+c cannot have two zeros.

(Use the Mean-value theorem, or some other argument.)

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