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bongbongtinhyeucuatoi
2 năm trước
cho tam thức bậc 2 f(x)=ax^2+bx+c, a khác 0. Chứng minh rằng nếu tồn tại một số thực a sao cho a.f(a)<=0 thì phương trình f(x) =0 luôn có nghiệm
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