# First Isomorphism Theorem for Groups Proof | Summary and Q&A

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November 30, 2014
by
The Math Sorcerer
First Isomorphism Theorem for Groups Proof

## TL;DR

If F is an onto homomorphism from G to K, then K is isomorphic to G mod the kernel of F, as proven by the First Isomorphism Theorem.

## Key Insights

• ❓ Isomorphism and the First Isomorphism Theorem are important concepts in abstract algebra.
• 🖐️ The kernel of a homomorphism plays a crucial role in determining the structure of the quotient group.
• 👥 The function S, defined in the content, serves as a bridge between the quotient group G mod the kernel of F and the target group K.
• 💨 The First Isomorphism Theorem provides a way to establish an isomorphism between groups based on a specific type of homomorphism.
• 👍 The proof presented demonstrates the steps involved in proving the isomorphism using the function S.
• 👥 The concepts discussed in the content offer a deeper understanding of group structures and their relationships through isomorphism.
• 🈸 The First Isomorphism Theorem is a fundamental result that has applications in various areas of mathematics.

## Transcript

prove that if F from G2 K is an onto homomorphism then K is isomorphic to G mod the kernel of fi so what is the kernel of fi well it's the set of all elements in G such that fi takes little G and sends it to the identity element in K so it's all the G's that fi maps to the identity element okay so to prove this we have to come up with a homomorphis... Read More

### Q: What is the kernel of Fi?

The kernel of Fi, denoted as H, is the set of all elements in G such that Fi takes an element G and sends it to the identity element in K.

### Q: How is the function S defined?

The function S takes a right coet, denoted as HX, from G mod the kernel of F and sends it to F of X. This function is used to prove the isomorphism.

### Q: What does it mean for the function S to be well-defined?

For the function S to be well-defined, it should produce the same result for two coets HX and HY that are equivalent. In other words, if HX = HY, then F(X) should be equal to F(Y).

### Q: Why do we need to show that S is a group homomorphism?

Showing that S is a group homomorphism ensures that the operation of multiplying two coets in G mod the kernel of F corresponds to the operation of multiplying their images in K under F.

### Q: How do we prove that the function S is onto?

To prove that S is onto, we take an element K in K and show that there exists a coet HX such that S(HX) = K. This is done by utilizing the onto property of F.

### Q: How is it shown that the function S is one-to-one?

To prove that S is one-to-one, we assume that S(HX) = S(HY) and show that this implies HX = HY. This relies on the fact that the kernel of F is the set of elements that are mapped to the identity element in K.

### Q: What is the significance of the First Isomorphism Theorem?

The First Isomorphism Theorem states that if F is an onto homomorphism from G to K, then K is isomorphic to G mod the kernel of F. It provides a fundamental result in abstract algebra for understanding isomorphisms.

### Q: How does the First Isomorphism Theorem relate to the concept of isomorphism?

The First Isomorphism Theorem shows that if a certain condition is met (existence of an onto homomorphism), then two groups can be considered isomorphic. It establishes a connection between the properties of group homomorphisms and the structure of groups.

## Summary & Key Takeaways

• The content discusses the concept of isomorphism and the First Isomorphism Theorem in abstract algebra.

• It explains that if F is an onto homomorphism from G to K, then K is isomorphic to G mod the kernel of F.

• The video demonstrates the proof by defining a function S that maps coets from G mod the kernel of F to K.