Assignment 3 Complex Numbers

Assignment 3
Complex Numbers
1. Use Euler’s Formula to convert the following complex numbers to standard form:
(a) e
iπ/2
(b) e
2πi/3
2. Rewrite z =
1 + √
3i
2
as an exponential using Euler’s formula and then compute z
6
.
Systems of Equations
3. Solve the following systems using an augmented matrix and performing elementary row operations
to get to reduced row echelon form (RREF):
a) 3x1 + 2x2 = −9 b) x1 + 2x2 + 3x3 = 1 c) x1 + 2x2 + 3x3 = 1
x1 + 4x2 = 7 x1 + x2 + x3 = 2 x1 − x2 + 2x3 = 2
x1 + 3x2 + 4x3 = 0 2x1 + x2 + 5x3 = 0
4. Consider two planes in R
3 defined by 3x1 + 2x2 − 4x3 = 1 and x1 + x2 − x3 = 1. Solve this system
of equations to determine if the planes intersect. If so, find a vector equation for the solution set.
What does this solution set represent geometrically?
5. Consider the vectors ~a1 = (2, −3, 4), ~a2 = (2, 6, 1), and ~a3 = (−2, −12, 1). To test for linear
independence, we are interested in the solution set of x1~a1 + x2~a2 + x3~a3 = 0 where x1, x2, and x3
are unknowns (i.e., variables). Expand this out and show it is equivalent to the system of equations
2x1 + 2x2 − 2x3 = 0
−3x1 + 6x2 − 12x3 = 0
4x1 + x2 + x3 = 0.
Solve the system of equations by converting the augmented matrix to RREF and determine if the
vectors are linearly independent. (Notice, we really didn’t need the augmented matrix here since
the right-hand sides stay zero. In other words, if we keep in mind that the right-hand sides are
always zero, we can just row-reduce the coefficient matrix.)
6. Consider the vectors ~a1 = (1, 0, 0), ~a2 = (1, 1, 0), and ~a3 = (0, 1, 1). To test for spanning, we need
to show that we can write any vector ~v = (v1, v2, v3) in R
3 as a linear combination of ~a1, ~a2, and
~a3. In other words, we wish to show that we can solve x1~a1 + x2~a2 + x3~a3 = ~v where x1, x2, and
x3 are unknowns (i.e., variables) for any values of v1, v2, and v3. Expand this out and show it is
equivalent to the system of equations
x1 + x2 = v1
x2 + x3 = v2
x3 = v3.
Solve the system of equations by converting the augmented matrix to RREF and determine if the
vectors span R
3
. (Notice, the right-hand sides end up being some linear combinations of v1, v2, and
v3 which are, in general, some non-zero numbers. Therefore, we need the RREF to be the identity
matrix otherwise the system is inconsistent.
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7. Before each Fall semester, the university bookstore places massive orders for the textbooks that will
be needs for the large first-year biology, chemistry, and physics courses. The following table gives
for three different years the number of books bought for each course along with the total cost.
Year Biology Chemistry Physics Cost
2016 1400 1800 600 $658,000
2011 1300 1700 500 $587,000
2006 1200 1600 400 $520,000
If we let xb, xc, and xp be the price for a single biology, chemistry, or physics textbook respectively
we can rewrite this information as a system of equations. What can you conclude about the price
of each individual textbook from year to year? (Tip: Start off your row reduction by scaling each
row by 1/100 to get easier numbers to work with.)
8. While searching through your attic, you find a bag of gold coins (yes, it turns out some of your
distant relatives were pirates, ARRR!). There are four types of gold coins and you’d like to know
how much gold you’ve just found so you need to work out the mass of each type of coin. However,
all you have is a balance scale and a few 10 g and 20 g weights. With some experimenting, you
discover the following:
A + B + C + D = 70 g
B + C = 30 g
2C + 2D = 90 g
4B + D = 80 g (1)
where A, B, C, and D are the unknown masses of each type of coin in grams. Determine the mass
of each type of coin. (Hint: Check your final values by plugging them back into the given system of
equations.)
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