tigonometry
posted by Pablo .
expres the following as sums and differences of sines or cosines
cos8t * sin2t
sin(a+b) = sin(a)cos(b) + cos(a)sin(b)
replacing by by b and using that
cos(b)= cos(b)
sin(b)= sin(b)
gives:
sin(ab) = sin(a)cos(b)  cos(a)sin(b)
Add the two equations:
sin(a+b) + sin(ab) = 2sin(a)cos(b)>
sin(a)cos(b)= 1/2 [sin(a+b) + sin(ab)]
who found trigonometry?
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