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verify identity

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1 Answer

You need the following two identities for this problem:
 
sec(x) = 1/cos(x)
sin2x + cos2x = 1
 
Now let's use them in your problem:
 
sin(x)sec(x) = [1-cos2(x)]/sin(x)cos(x)
 
sin(x)/cos(x) = sin2(x)/sin(x)cos(x)       [sec(x) = 1/cos(x), 1-cos2(x)=sin2(x)]
 
sin(x)/cos(x) = sin(x)/cos(x)
 
QED

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