Exam 1 Math 1360 September 30, 2019
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Exam 1 Math 1360 September 30, 2019
Work each problem on a separate page
Staple in upper LH corner when you hand in
Make plots BIG [at least 1/2 page] and clear. Give clear and complete work. Work is graded-not just final answers.
Full justifications are needed for credit. Calculators and scrap paper allowed
1. Write down Richardson’s model of arms races and give the as- sumption yielding each term.
2. For the system below, sketch the nullclines, trajectory directions, equilib- ria and a few trajectories:
x′ = y − x2 and y′ = x − y.
3. Consider the second order equation
θ′′ + θ′ + sin θ = 0.
a. Write it as a first order system in the standard way. b. This system will have an equilibrium at (0,0). Find the linearization there and classify it.
4. The number of twitter users N(t) for several years is listed below [in millions]. a. calculate [explain how] and fill in consistent approximations to the entries underlined for the years 2011,2013,2015. b. Plot the data on (N,N′ /N) axes. From this plot give an estimate of the ultimate maximum number of twitter users. Explain how you arrived at this estimate.
year N(t) N′ (t) N′ /N
2010 49
2011 ____________ ___________
2012 151
2013 ______________ ____________
2014 271
2015 ____________ ____________
2016 313
2023-09-28