- Forums
- Homework Help
- Calculus and Beyond Homework Help
- Thread startertlkieu
- Start date
- Tags
- InequalitiesTriangleTriangle inequality
In summary, the conversation discussed proving the triangular inequality and using it to prove a related inequality. The first part showed that |x + y| ≤ |x| + |y| and the second part split the proof into two cases. The last part, (c), is still in progress and involves using the triangle inequality to show that if certain conditions are met, then |(x + y) − (a + b)| < c.
- #1
tlkieu
- 8
- 1
Just wondering if anyone could confirm if I've headed in the right direction with these
(a) Prove the triangular inequality: |x + y| ≤ |x| + |y|.
(b) Use triangular inequality to prove |x − y| ≥ ||x| − |y||.
(c) Show that if |x − a| < c/2 and |y − b| < c/2 then |(x + y) − (a + b)| < c.
So for (a):
∣x+y∣∣^2 = (x+y)^2
= x^2 + 2xy + y^2
= |x|^2 + 2xy + ∣y∣^2
≤ |x|^2 + 2∣xy∣ + ∣y∣^2
= |x|^2 + 2|x|⋅∣y∣ + ∣y∣^2
= (|x|+∣∣y∣∣)^2
Which shows ∣x+y∣ ≤ |x| + ∣y∣
For (b):
I split it into two proofs
In case (1): If |x| ≥ ∣y∣ we have:
∣|x| − ∣y∣∣ = |x|− ∣y∣, and the proof is finished.
For case (2): If ∣y∣ ≥ |x|:
∣y−x∣ ≥ ∣y∣ − |x| = ∣∣y∣ − |x|∣
That is what I have so far and part (c) I'm not too sure how to approach that one
Physics news on Phys.org
- #2
LCKurtz
Science Advisor
Homework Helper
Insights Author
Gold Member
- 9,568
- 775
tlkieu said:
Just wondering if anyone could confirm if I've headed in the right direction with these
(a) Prove the triangular inequality: |x + y| ≤ |x| + |y|.
(b) Use triangular inequality to prove |x − y| ≥ ||x| − |y||.
(c) Show that if |x − a| < c/2 and |y − b| < c/2 then |(x + y) − (a + b)| < c.So for (a):
∣x+y∣∣^2 = (x+y)^2
= x^2 + 2xy + y^2
= |x|^2 + 2xy + ∣y∣^2
≤ |x|^2 + 2∣xy∣ + ∣y∣^2
= |x|^2 + 2|x|⋅∣y∣ + ∣y∣^2
= (|x|+∣∣y∣∣)^2
Which shows ∣x+y∣ ≤ |x| + ∣y∣For (b):
I split it into two proofs
In case (1): If |x| ≥ ∣y∣ we have:
∣|x| − ∣y∣∣ = |x|− ∣y∣, and the proof is finished.For case (2): If ∣y∣ ≥ |x|:
∣y−x∣ ≥ ∣y∣ − |x| = ∣∣y∣ − |x|∣That is what I have so far and part (c) I'm not too sure how to approach that one
They look correct. For the last one take the left side of what you are trying to prove and break it up into two terms similar to what you are given and use the triangle inequality on it.
1. What are the Triangle Inequalities?
The Triangle Inequalities are a set of mathematical principles that describe the relationship between the sides and angles of a triangle. They state that the sum of any two sides of a triangle must be greater than the third side, and the difference between any two sides must be less than the third side.
2. Why are the Triangle Inequalities important?
The Triangle Inequalities are important because they provide a way to determine if a set of three given side lengths can form a triangle. They also help in proving various geometric theorems and solving real-world problems involving triangles.
3. How do the Triangle Inequalities relate to the Pythagorean Theorem?
The Triangle Inequalities are closely related to the Pythagorean Theorem, which states that in a right triangle, the square of the length of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides. The Triangle Inequalities help to determine if the given side lengths can form a triangle, and if they can, then the Pythagorean Theorem can be used to find the length of the hypotenuse.
4. Can the Triangle Inequalities be applied to any type of triangle?
Yes, the Triangle Inequalities can be applied to any type of triangle, whether it is a right triangle, an acute triangle, or an obtuse triangle. They hold true for all triangles, regardless of their angles and side lengths.
5. How can the Triangle Inequalities be used to solve real-world problems?
The Triangle Inequalities can be used to solve real-world problems involving triangles, such as finding the shortest distance between two points, determining the maximum area of a triangle with a fixed perimeter, or calculating the minimum length of a ladder needed to reach a certain height on a building. They provide a way to analyze and understand the relationships between the sides and angles of a triangle in practical scenarios.
Similar threads
Integration problem using inscribed rectangles
- Calculus and Beyond Homework Help
- Replies
- 14
- Views
- 194
What is the name of this inequality?
- Calculus and Beyond Homework Help
- Replies
- 2
- Views
- 827
Prove ##(a\cdot b)\cdot c =a\cdot (b \cdot c)## using Peano postulates
- Calculus and Beyond Homework Help
- Replies
- 1
- Views
- 452
How should I find the nontrivial stationary paths?
- Calculus and Beyond Homework Help
- Replies
- 10
- Views
- 296
Prove if ##x<0## and ##y<z## then ##xy>xz## (Rudin)
- Calculus and Beyond Homework Help
- Replies
- 2
- Views
- 588
Prove ##(a+b)\cdot c=a\cdot c+b\cdot c## using Peano postulates
- Calculus and Beyond Homework Help
- Replies
- 3
- Views
- 506
Prove ##(a+b) + c = a + (b+c)## using Peano postulates
- Calculus and Beyond Homework Help
- Replies
- 9
- Views
- 1K
Why is this not a general solution to this nonlinear DE?
- Calculus and Beyond Homework Help
- Replies
- 5
- Views
- 267
Help me prove integral answer over infinitesimal interval
- Calculus and Beyond Homework Help
- Replies
- 9
- Views
- 534
Determine whether ## S[y] ## has a maximum or a minimum
- Calculus and Beyond Homework Help
- Replies
- 18
- Views
- 1K
- Forums
- Homework Help
- Calculus and Beyond Homework Help