4) Consider ? ⊆ ℝ × ℝ with {(?,?)|?2 =
?2}. Prove that ? is an...
4) Consider ? ⊆ ℝ × ℝ with {(?,?)|?2 =
?2}. Prove that ? is an equivalence relation, and
concisely characterize how its equivalence classes are different
from simple real-number equality.
Consider the function ?: (−1,1) × (−1,1) → ℝ given by ?(?, ?) =
sin(?? + ?? + ?2 ).
1. Find a bound for the directional derivative of ? in any
direction, i.e. find a constant ? such that |???(?, ?)|
≤ ? for all (?, ?) ∈ (−1,1) × (−1,1) and ? ∈ ℝ 2 with
|?| = 1.
Define a function ?∶ ℝ→ℝ by
?(?)={?+1,[?] ?? ??? ?−1,[?]?? ????
where [x] is the integer part function. Is ? injective?
(b) Verify if the following function is
bijective. If it is bijective, determine its inverse.
?∶ ℝ\{5/4}→ℝ\{9/4} , ?(?)=(9∙?)/(4∙?−5)
Topology question:
Show that a function f : ℝ → ℝ is continuous in the ε − δ
definition of continuity if and only if, for every x ∈ ℝ and every
open set U containing f(x), there exists a neighborhood V of x such
that f(V) ⊂ U.
4.Consider events A and B, neither of which are impossible
events. Prove the following
statements.
A)? ? ? = 1 − ?(?|?)
B)If ? ? ? ? = ? ? ∩ ? , then A and B must be
independent events.
Prove these scenarios by mathematical induction:
(1) Prove n2 < 2n for all integers
n>4
(2) Prove that a finite set with n elements has 2n
subsets
(3) Prove that every amount of postage of 12 cents or more can
be formed using just 4-cent and 5-cent stamps