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Hey,

this proof has been annoying me all day. i don't understand what its asking do and have no idea how to solve it. The proof asks:

Prove that the altitudes of a traingle are concurrent.

Here is the diagram for it:

http://img246.imageshack.us/img246/1899/pfji4.jpg [Broken]

[tex]

\begin{array}{l}

\overrightarrow {FA} = {\bf{a}} \\

\overrightarrow {FC} = {\bf{c}} \\

\overrightarrow {FB} = {\bf{b}} \\

\end{array}

[/tex]

Im also told to use the fact that

[tex]{\bf{a}} \cdot \overrightarrow {BC} = 0[/tex]

and

[tex]{\bf{b}} \cdot \overrightarrow {AC} = 0[/tex]

to prove that [tex]\overrightarrow {CF}[/tex] is perpendicualr to [tex]\overrightarrow {AB}[/tex]

thanks to anyone who understands what this is asking me to do and post back helpful infomation,

Pavadrin

this proof has been annoying me all day. i don't understand what its asking do and have no idea how to solve it. The proof asks:

Prove that the altitudes of a traingle are concurrent.

Here is the diagram for it:

http://img246.imageshack.us/img246/1899/pfji4.jpg [Broken]

[tex]

\begin{array}{l}

\overrightarrow {FA} = {\bf{a}} \\

\overrightarrow {FC} = {\bf{c}} \\

\overrightarrow {FB} = {\bf{b}} \\

\end{array}

[/tex]

Im also told to use the fact that

[tex]{\bf{a}} \cdot \overrightarrow {BC} = 0[/tex]

and

[tex]{\bf{b}} \cdot \overrightarrow {AC} = 0[/tex]

to prove that [tex]\overrightarrow {CF}[/tex] is perpendicualr to [tex]\overrightarrow {AB}[/tex]

thanks to anyone who understands what this is asking me to do and post back helpful infomation,

Pavadrin

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