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(a+b)^2 + (a-b)^2 = (a+b) * (a+b) + ( a-b) * (a-b) =( a^2+ab + ab + b^2 ) +( a^2 -ab - ab - b^2)=
=a^2 + b^2 + 2ab + a^2 - b^2 -2ab = 2a^2
2a^2 *( 2a^2 - 2b^2) = 4a^4 -4ab^4
Obrazek 2
(x-3y)^2 - (x+3y)^2 = ( x-3y) * (x-3y) - (x+3y) + (x+3y) = (x^2 -3xy -3xy +9y^2) - (x^2 +3xy+3xy+9y^2) = x^2 -6xy+9y^2 - x^2 -3xy - 3xy-9y^2 = -12xy
-12xy + 12xy = 0