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Answer:
A, B
Explanation:
The equation is equivalent to ...
cos(x -π/7) = -(√2)/2
x -π/7 = arccos(-(√2)/2) = {3π/4, 5π/4} . . . . . cosine is negative in QII and QIII
x = {3π/4 +π/7, 5π/4 +π/7} +2nπ . . . . . matches A and B
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