remember some triangle functions
(1)sinA+sinB=2sin((A+B)/2)cos((A-B)/2);
(2)sinA-sinB=2cos((A+B)/2)sin((A-B)/2);
(3)cosA+cosB=2cos((A+B)/2)cos((A-B)/2);
(4)cosA-cosB=-2sin((A+B)/2)sin((A-B)/2);
I haven’t finish today’s learning plan-only finished 4 pages of 10 pages.That’s ok,I am a lazy man today.I am not a machine.
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