6. Let ABC be an acute-angled triangle. The feet of the altitudes from
internet until 8am GMT on Saturday 3 December.
A, B and C are D, E and F respectively. Prove that DE +DF ≤ BC
Do not turn over until told to do so.
and determine the triangles for which equality holds.
The altitude from A is the line through A which is perpendicular to
BC. The foot of this altitude is the point D where it meets BC. The
other altitudes are similarly defined.
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