Real numbers a and b are such that sin ( ln i i ) = a + i b . Find a + b .
Note: We are taking the standard principal branch of the complex logarithm.
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s i n l o g i i = s i n l o g ( e i 2 π ) i = s i n l o g ( e − 2 π ) = s i n ( − 2 π ) = − 1
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sin ( ln ( i i ) ) = ? e i π = − 1 e 2 i π = i ⎝ ⎜ ⎛ e 2 i π ⎠ ⎟ ⎞ i = i i sin ( ln ( i i ) ) = sin ⎝ ⎜ ⎛ ln ⎝ ⎜ ⎛ e 2 i π ⎠ ⎟ ⎞ i ⎠ ⎟ ⎞ = sin ⎝ ⎜ ⎛ i ln ⎝ ⎜ ⎛ e 2 i π ⎠ ⎟ ⎞ ⎠ ⎟ ⎞ = sin ( i 2 i π ln ( e ) ) = sin ( − 1 × 2 π ) = − sin ( 2 π ) = − 1 ∴ − 1 = a + i b ⟹ a = − 1 , b = 0 ⟹ a + b = − 1