9514 1404 393
Answer:
A, B
Step-by-step 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
