Received the following question today:

In general it only takes two lines to plot a trendline or support or resistance however most traders I think would agree that the more points you have the more valid the trend or support/resistance line is thought to be.

For more information on Trends and Support/Resistance see module 1 of the InformedTrades.com Free Trading Course and in particular the lessons from that module Dow Theory and Trends and Support and Resistance.

Below you can find two additional links from Trader Mike on the subject:

Drawing Trendlines » Trader Mike

More on Trendlines » Trader Mike

Below you can find another good post on this from AfraidtoTrade.com:

Afraid to Trade.com Blog - Overcoming Fears » Assessing the Validity of Trendlines

Hope that helps. If anyone else has anymore thoughts on this or good resources related to this please feel free to post them below.

Best Regards,
Dave