Problem 10 Let f_n:R-->R be differentiable for each n
with |f'_n(x)|<=1 for all n and x. Assume f_n(x)-->g(x) :
for all x. Prove that g is continuous.
Problem 11 Show that the differential equation x'=3x^2 has no solution such that x(0)=1 and x(t) is defined for all real numbers t.
Problem 12 Let X
R be a nonempty connected set of real numbers. If every element of X is rational, prove X has only one element.
Problem 13 Consider the following four types of transformations:
z--> z+b;z--> 1/z;z--> kz; k
0
z--> :frac{az+b}{cz+d} ad-bc
0
Here, z s a variable complex number and the other letters denote constant complex numbers. Show that each transformation takes circles to either circles or straight lines.
Problem 14 If a and b are complex numbers and a
0, the set a^b consists of those complex numbers c having a logarithm of the form bx, for some logarithm x of a. (That is, e^{bx}=c and e^x=a for some complex number x.) Describe set a^b when a=1 and b=1/3+i.
Problem 15 Let f have continuous partial derivatives and satisfy
| :frac{df}{dx_j}(x) |
K
for all x=(x_1..x_n) , . Prove that
|f(x)-f(y)|
n^{1/2}K ||x-y||
Problem 17 Let be the set of 3*3 real matrices with zeros below the diagonal and ones on the diagonal.
Prove G is a group under matrix multiplication.
Determine the center of G.
Problem 18 Suppose the complex number z is a root of a polynomial of degree with rational coefficients. Prove that 1/z is also a root of a polynomial of degree n with rational coefficients.
Problem 19 Let be a real 3*3 matrix such that M^3=I,M
I .
What are the eigenvalues of M?
Give an example of such a matrix.
Problem 20 Let C^3 denote the set of ordered triples of complex numbers. Define a map by
F(x,y,z)=(x+y+z,xy+yz+zx,xyz)
Prove that F is onto but not one-to-one.