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can someone show me how to solve this identity:
csc^4(x)-cot^4(x)=(2csc^2)-1
note: you can only work on one side
additional info: 1+cot^2(x)=csc^2(x), 1+tan^2(x)=sec^2(x)
 Nov 15, 2013
 #1
avatar+118653 
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can someone show me how to solve this identity:
csc^4(x)-cot^4(x)=(2csc^2)-1
note: you can only work on one side
additional info: 1+cot^2(x)=csc^2(x), 1+tan^2(x)=sec^2(x)

I am having problems with this one
You have left out an x on the right hand side,
Could you just double check that the rest of the question is written down correctly.
Thanks.
 Nov 15, 2013
 #2
avatar+118653 
0
csc^4(x)-cot^4(x)= (2csc^2(x))-1

LHS = [ 1 / (sin 2x) 2 ] - [ (cos 2x) 2 / (sin 2x) 2 ]

= [ 1 - (cos 2x) 2 ] / (sin 2x)

= [ (1-cos 2x)(1+cos 2x) ] / (1-cos 2x) 2

= (1+cos 2x) / (1-cos 2x)

= (1+cos 2x) / sin 2x

= (1+1-sin 2x) / sin 2x

= (2-sin 2x) / sin 2x

= 2/sin 2x - sin 2x/sin 2x

= 2csc 2x -1

=RHS QED
 Nov 15, 2013

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