Could someone show me what i'm doing wrong?

Question

81-4r^2

 

so i tried breaking them up and got (9-2^r) (9+2^r)

 

or do i have to break it up further? could someone help me i really want to learn this

Answer 1

Latrice,

 

Jim is right. What you call 'breaking them up' is normally referred to as factoring.  The difference of 2 squares is one of the ways to factor. you have probably seen something like this:

 

a² - b² = (a + b) (a - b) 

 

In words it says that 'something squared' minus 'something else squared' is equal to 'something' plus 'something else' times 'something' minus 'something else. Get it? 'something' is 'a' and 'something else' is 'b'.

 

In the expression you input [ 81-4r² ] you first have to realize that 81 = 9² and 4r² = (2r)².

 

This makes your expression = 9² - (2r)² . Making 9 'something' and 2r 'something else'

 

You correctly factored it into (9 + 2r) (9 - 2r).

 

If you have problems with it you might try multiplying (like using FOIL) (a + b)(a - b).

 

Let me know if this helps.

Answer 2

Looks to me as though you factored the expression using the difference of two squares rule correctly.

 

Jim