Question 766558
Solve: cos^4a+cos^2a=1
sub x for cos^2
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{{{x^4 + x^2 - 1 = 0}}}
*[invoke solve_quadratic_equation 1,1,-1]
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cos^2 = 0.618034
cos =~ 0.78615
a =~ 38.1727 degs (principal value)