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(a-b)(-a-b)

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2 Answers

FOIL
 
First (a)(-a) = -a^2
Outside (a) (-b) = -ab
Inside (-b)(-a) = ab
Last (-b) (-b) = b^2
 
-a^2 - ab + ab + b^2
 
Answer:
 
-a^2 + b^2
 
Alternatively,
(a-b)(-a-b) = (a-b)-(a+b) = -(a-b)(a+b) = - (a^2 - b^2)   (diff. of 2 squares)
                                                           = -a^2 + b^2
 
Hope this helps.
Hi Suraj;
(a-b)(-a-b)
We need to FOIL...
FIRST...(a)(-a)=-a2
OUTER...(a)(-b)=-ab
INNER...(-b)(-a)=ab
LAST...(-b)(-b)=b2
-a2-ab+ab+b2
-a2+b2

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