Odpowiedź:
[tex]4-(x+7)(1-x)=x^2-9\\\\4-(x-x^2+7-7x)=x^2-9\\\\4-x+x^2-7+7x=x^2-9\\\\-3+6x+x^2=x^2-9\\\\6x+x^2-x^2=-9+3\\\\6x=-6\ \ /:6\\\\x=-1[/tex]
