Trig/precalc
posted by Joe .
Cos[x + (7 Pi)/4] + Cos[x  (7 Pi)/4] = 1

cos(x) cos(7pi/4)  sin(x) sin(7pi/4) + cos(x) cos(7pi/4) + sin(x) sin(7pi/4) = 1
2cos(x) cos(7pi/4) = 1
2cos(x) * 1/√2 = 1
cos(x) = 1/√2
x = pi/4 or 7pi/4
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