Simple pendulum - displacement increase

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ward.o.j
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<Moderator's note: Moved from a technical forum and therefore no template.>

A simple pendulum of length l (supported by a light, rigid rod) is released from rest at a small angle to the upward vertical.

Show that the time taken for the angular displacement to increase by a factor of 10 is approximately (l/g)1/2ln20.

This is from chapter 2 of Kibble. There's a section which suggests writing x=½Aept+½Be-pt as one version of the general solution to the equations of motion which seems promising, but I can't see how this leads to the value in the question, or if I'm just barking up the wrong tree.

Any advice on how to proceed would be much appreciated.

P.S. If anyone would like to shed some light for me on how to post equations so that they are more readable than the one's I've posted, I'd be grateful for that as well.
 
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