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nguyendonglqdonline
2 năm trước
cho tam giác ABC với ba đường cao AA', BB', CC'. gọi H là trực tâm của tam giác đó. Chứng minh rằng $\frac{HA'}{AA'}$ + $\frac{HB'}{BB'}$ + $\frac{HC'}{CC'}$ = 1
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