How do you expand (-x-y)^2 ?

Question

I know it'll expand by the (a-b)^2 formula but I'm confused with the minus symbol.

Please explain in detail, thankyou.

Answer 1

Edited solution showing a third way to expand:

 

You can factor out the minus sign:

 

(-x - y)² = [(-1)(x + y)]² = (-1)²(x + y)² = (1)(x² + 2xy + y²)

 

Or you can do it this way:

 

(-x - y)² = [(-x) + (-y)]² = (-x)² + 2(-x)(-y) + (-y)² = x² + 2xy + y²

 

And yet another way to do it, if you want to use the (a - b)² formula:

 

(-x - y)² = [(-x) - y]² = (-x)² - 2(-x)(y) + (-y)² = x² + 2xy + y²

Answer 2

(-x - y)² = (-x - y)(-x - y) = x² + 2xy + y²