Can you explain me this notable product?

Question

#(-2-x)^2#

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Answer 1 · 2018-05-08T11:46:17

# x^2+2x+1#

#(-1-x)^2=(-1-x)(-1-x)#

-1 times everything in the second bracket
#=> 1+x#

then #-x# times everything in the second bracket
#=> x+x^2#

then collect like terms
#=>1+x+x+x^2 = x^2+2x+1#