# expanding (x+y)^2 (from no algebra to abstract algebra) | Summary and Q&A

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June 28, 2022
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blackpenredpen
expanding (x+y)^2 (from no algebra to abstract algebra)

## TL;DR

(x+y)^2 is not equal to x^2+y^2; instead, it expands to x^2+2xy+y^2, which is important to remember in abstract algebra.

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### Q: Why does (x+y)^2 not equal x^2+y^2?

The expansion of (x+y)^2 using the foil method shows that it is equal to x^2+2xy+y^2. The mistake in thinking it equals x^2+y^2 is due to the commutative property, which may not hold in abstract algebra.

### Q: How can the area of a square help understand the expansion of (x+y)^2?

By visualizing (x+y) as the length and width of a square, the expansion can be understood as adding the areas: x^2 (area of a square with side x), 2xy (twice the area of a rectangle with sides x and y), and y^2 (area of a square with side y).

### Q: What are the definitions of x and x^2 in calculus?

In calculus, x is defined as the integral of 1 from 0 to x. x^2 is defined as the integral of 2t from 0 to x. These definitions are used to explain the expansion of (x+y)^2 in terms of integrals.

### Q: How is the expansion of (x+y)^2 derived using abstract algebra?

By using the definitions of x and x^2 as integrals, the expansion is written as the integral of 2t from 0 to x+y. Through substitution and properties of integrals, it simplifies to x^2+2xy+y^2, which is the correct expansion.

## Summary & Key Takeaways

• The content explains the correct expansion of (x+y)^2 as x^2+2xy+y^2.

• It demonstrates the use of the foil method to expand the expression.

• The video also introduces the concept of abstract algebra and how it challenges the traditional understanding of (x+y)^2.