Question

find the product of (y-1) y+1)
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Answer 1

Answer- The above question is from the chapter 'Algebraic Expressions'.

Important identities:

1) (a+b)² = a² + 2ab + b²

2) (a-b)² = a² - 2ab + b²

3) (a+b) (a-b)= a² - b².

Let's take an example of (2+3) (2-3).

This is in the form (a+b) (a-b) where a= 2 and b= 3. By using identity of (a+b) (a-b)= a² - b²,

(2+3) (2-3)= 2² - 3²

               = 4 - 9

               = -5

If we check this by simple calculation,

(2+3) (2-3)= 5 × -1 = -5

Given question: What is the answer of (y-1) (y+1) ?

Solution: This is in the form (a+b) (a-b) where a= y and b= 1. By using identity of (a+b) (a-b)= a² - b²,

(y-1) (y+1)

= y² - 1

∴(y-1) (y+1) = y² - 1