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[Hlib2]

I easily converted the expression manually:
cos(3×X)+cos(X)=2×cos(2×X)×cos(X).
But I couldn`t do it either in afx-2.0+/graph100+ or in ti-v200. I may have forgotten some of the CAS features of these calculators. I would be grateful for a hint on how to do this in CASIO.