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• = lim [ (-msinmx + nsinnx ) / (2x) ] = lim [ (-m^2 cosmx +n^2 cosnx ) / 2 ] = (n^2-m^2)/2 [ some purists might not like the double use of l'hopital but if f''/g'' converges, f'/g' converges to same limit .. without doing a normal proof tha…

  in lim x-->0 [cos(mx) - cos(nx)] / x^2? Comment by hustolemyname May 2021
• = lim [ (-msinmx + nsinnx ) / (2x) ] = lim [ (-m^2 cosmx +n^2 cosnx ) / 2 ] = (n^2-m^2)/2 [ some purists might not like the double use of l'hopital but if f''/g'' converges, f'/g' converges to same limit .. without doing a normal proof tha…

  in lim x-->0 [cos(mx) - cos(nx)] / x^2? Comment by hustolemyname May 2021