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find all solutions of the given equation in the interval [0,2pi] cosx=cos3x
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\[\pi\] would work
i guess 0 would work as well. and maybe \[\frac{\pi}{2}\]
maybe write 4cos^3(x) - 3cos(x) = cos(3x) (as this is an identity i think (correct me if i am wrong) Then obviously: cos(x) = 4cos^3(x) - 3cos(x) hence 0 = 4cos(x)(cos^2(x) - 1) so you can tell right away that all the places where cos(x) vanishes in that interval are solutions. Next solve cos^2(x) -1 = 0 for x to find the others
@Callum, yes, that is the correct identity. This is how I would do the problem.
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