(x+y–5)(x-y+5)

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(x+y–5)(x-y+5)(x+y–5)(x-y+5)(x+y–5)(x-y+5)(x+y-5)(x-y+5)=(x+y)²-5²=x²+y²+2xy-25

(x+y–5)(x-y+5)
(x+y–5)(x-y+5)

(x+y–5)(x-y+5)
(x+y-5)(x-y+5)
=(x+y)²-5²
=x²+y²+2xy-25