Factor completely.

Question

1/81r² (fraction) - 16/25s² (fraction)

 

a. (r+s)[ 1/81r - 16/25s]

b. [1/9r - 4/5s]²

c. [1/9r + 4/5s][1/9r - 4/5s]

d. [1/9r + 4/5s]²

 

Answer 1

Hi Amanda,

 

This is same as "difference of 2 squares"  x² - y² = (x+y) (x-y)

 

For yours: 1st [1 /(81r²) is square], 2nd [16 /(25s²) is square].

 

√1 = 1,      √81r² = 9r  

 

√16 = 4,    √25s² = 5s

 

  1               4             1       4           1       4

------   -   ------   =   (------ + -------) (------ - ------)

81r²          25s²         9r      5s         9r      5s

 

So, the answer is c. [1/9r + 4/5s][1/9r - 4/5s]

 

There you have it.  I hope you understood.

 

 

Yohan Chu   (LV  NV)

 

Answer 2

=c. [1/9r + 4/5s][1/9r - 4/5s]