1) a) Let k ≥ 2 and let G be a k-regular bipartite
graph. Prove that G has no cut-edge. (Hint: Use the bipartite
version of handshaking.)
b) Construct a simple, connected, nonbipartite 3-regular graph
with a cut-edge. (This shows that the condition “bipartite” really
is necessary in (a).)
2) Let F_n be a fan graph and Let a_n = τ(F_n) where τ(F_n) is
the number of spanning trees in F_n. Use deletion/contraction to
prove that a_n = 3a_n-1 - a_n-2...
Let n be a positive integer. Let S(n) = n sigma j=1 ((1/3j − 2)
− (1/3j + 1)). a) Compute the value of S(1), S(2), S(3), and S(4).
b) Make a conjecture that gives a closed form (i.e., not a
summation) formula for the value of S(n). c) Use induction to prove
your conjecture is correct.
Let f(n,k) be the number of equivalence relations with k classes
on set with n elements.
a) What is f(2,4)?
b) what is f(4,2)?
c) Give a combinational proof that f(n,k) = f(n-1,k-1)+k *
f(n-1,k)
4. Let n ≥ 8 be an even integer and let k be an integer with 2 ≤
k ≤ n/2. Consider k-element subsets of the set S = {1, 2, . . . ,
n}. How many such subsets contain at least two even numbers?
Let S = {2 k : k ∈ Z}. Let R be a relation defined on Q− {0} by
x R y if x y ∈ S. Prove that R is an equivalence relation.
Determine the equivalence class
Let k be an integer satisfying k ≥ 2. Let G be a connected graph
with no cycles and k vertices. Prove that G has at least 2 vertices
of degree equal to 1.
Let P(n) := ” If n^3 is odd then n is also odd.” I.e., if ∃k ∈
Z, n3 = 2k + 1, ∃b ∈ Z, n = 2b + 1
a) Prove P(n) by contraposition
b) Prove P(n) contradiction
c) Prove P(n) using induction
The production function is f(K,N) = N/2 + √ K, where N is the
amount of labor used and K the amount of capital used. (a) What is
returns to scale of this production function? What is the marginal
product of labor? (b) In the short run, K¯ = 4. Labor is variable.
On the graph, draw output as a function of labor input in the short
run in blue. Draw the marginal product of labor as a function of...