how do i find the sinusoidal equations for the following graphs?

Question

graph number one(tides):
http://www.epa.qld.gov.au/media/storms/graphs/mackay_tide.jpg

graph number two(2nd graph on the page, monthly temperature):
http://www.bom.gov.au/cgi-bin/climate/cgi_bin_scripts/map_script_new.cgi?33119

Answer 1

A sinusoid is characterized by its amplitude and its period. Your first graph has a variable amplitude, so you might want to take an average.