(a-b)(-a-b)

Question

expand using identities

Answer 1

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.

Answer 2

Suraj,

 

(a-b)(-a-b)

 

= (a-b) * -(a+b) [ taking minus common as both a and b have minus sign]

= -(a-b)(a+b)

= -(a² -b²) [Using identity (a+b)(a-b) =a²-b² ]

= -a² +b²

 

Answer 3

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