1. ## Expand this

((r-1)^2)(r+1)

How do I expand this? Thanks,

JN

2. Originally Posted by Jim Newt
((r-1)^2)(r+1)

How do I expand this? Thanks,

JN
Rewrite the term:

$(r-1)^2 \cdot (r+1)= (r-1)(r-1)(r+1) = (r-1)(r^2-1) = r^3-r^2-r+1$

3. Hello,

Originally Posted by Jim Newt
((r-1)^2)(r+1)

How do I expand this? Thanks,

JN
You can do this in two ways :

- develop $(r-1)^2$ by using the identity : (a-b)²=a²-2ab+b², then multiply by (r+1). But this will make a multiplication 3 terms by 2 terms

- write : $(r-1)^2=(r-1)(r-1) \implies ((r-1)^2)(r+1)=(r-1){\color{red}(r-1)(r+1)}$

Use the identity : (a-b)(a+b)=a²-b²
Then, it will be a multiplication 2 terms by 2 terms, which is more beautiful