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dat y=f(x),thi f(x) la ham phan thuc huu ti nen f(x) lien tuc tren R f(-4)=-19/3;f(-1)=7/6=>f(-4)f(-1)<0 => pt co it nhat 1 nghiem x\in (-4;-1) (3*) f(-1)=7/6;f(0)=-1=>f(-1)f(0)<0 pt f(x) co it nhat 1 nghiem x\in (-1;0) (2*)
voi f(0)= -1 ,f(2)=5 =>f(0)f(2)<0 pt f(x) co it nhat 1 nghiem x\in (0;2) (*) tu *,2*,3*=> pt f(x) co 3 nghiem pb
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