Question 172849
sin2x + cos(x)=0
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sin^2 = 1-cos^2
1-cos^2 + cos = 0
cos^2 - cos - 1 = 0
A quadratic in cos(x)
*[invoke solve_quadratic_equation 1,-1,-1]
cos(x) = 1/2 + sqrt(5)/2 =~1.618
cos>1 is not a real number, so ignore it.
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cos(x) = 1/2 - sqrt(5)/2 =~ -0.618
x = 128.173º