Trig/precalc

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Cos[x + (7 Pi)/4] + Cos[x - (7 Pi)/4] = 1

• Trig/precalc -

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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