melmonty1 melmonty1

20-08-2016
Mathematics

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prove that cos(a-b) - cos(a+b) = 2sina sinb

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dalendrk dalendrk

21-08-2016

We know:
cos(a - b) = cos(a)cos(b) + sin(a)sin(b)
cos(a + b) = cos(a)cos(b) - sin(a)sin(b)

cos(a - b) - cos(a + b) = 2sin(a)sin(b)

L = cos(a)cos(b) + sin(a)sin(b) - (cos(a)cos(b) - sin(a)sin(b))

= cos(a)cos(b) + sin(a)sin(b) - cos(a)cos(b) + sin(a)sin(b)

= 2sin(a)sin(b) = R

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