The equation above holds true for positive integers and , with and square-free.
Find .
Clarifications :
denotes Euler's number , .
.
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Factoring out e i 4 π :
e i 4 π ( e − i 8 π + e i 8 π )
Now this problem is purely computational. Using Euler's Formula, the question becomes
( cos ( 4 π ) + i sin ( 4 π ) ) ( cos ( − 8 π ) + cos ( 8 π ) + i ( sin ( − 8 π ) + sin ( 8 π ) ) )
Using the facts that sine is an odd function and cosine is even function:
( cos ( 4 π ) + i sin ( 4 π ) ) ( 2 cos ( 8 π ) )
Compute cos ( 8 π ) using the cos ( 2 x ) = 2 1 + cos x , an identity that can be derived from the power reducing formula. Evaluating cos ( 8 π ) and cos ( 4 π )
( 2 + 2 ) ( 2 1 + i 2 1 )
Factoring out 2 1 :
⎝ ⎛ 2 2 + 2 ⎠ ⎞ ( 1 + i )
This is the form asked for by the problem. Evaluating α a × β b × γ , the answer is
8