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Lt subscript x not stretchy rightwards arrow 0 end subscript fraction numerator cos a x minus cos b x over denominator x squared end fraction

  1. fraction numerator a squared minus b squared over denominator 2 end fraction
  2. fraction numerator b squared minus a squared over denominator 2 end fraction    
  3. fraction numerator a squared plus b squared over denominator 2 end fraction    
  4. 2 open parentheses a squared minus b squared close parentheses    

The correct answer is: fraction numerator b squared minus a squared over denominator 2 end fraction


    limit as x rightwards arrow 0 of open parentheses fraction numerator cos a x minus cos b x over denominator x squared end fraction close parentheses
equals limit as x rightwards arrow 0 of open parentheses fraction numerator negative 2 sin open parentheses begin display style fraction numerator a x plus b x over denominator 2 end fraction end style close parentheses sin open parentheses begin display style fraction numerator a x minus b x over denominator 2 end fraction end style close parentheses over denominator x squared end fraction close parentheses
equals negative 2 limit as x rightwards arrow 0 of open parentheses fraction numerator sin open parentheses begin display style fraction numerator a plus b over denominator 2 end fraction end style x close parentheses sin open parentheses begin display style fraction numerator a minus b over denominator 2 end fraction end style x close parentheses over denominator open parentheses x close parentheses open parentheses x close parentheses end fraction close parentheses
equals negative 2 open parentheses fraction numerator a plus b over denominator 2 end fraction close parentheses open parentheses fraction numerator a minus b over denominator 2 end fraction close parentheses limit as x rightwards arrow 0 of open parentheses fraction numerator sin open parentheses begin display style fraction numerator a plus b over denominator 2 end fraction x end style close parentheses sin open parentheses begin display style fraction numerator a minus b over denominator 2 end fraction x end style close parentheses over denominator open parentheses x close parentheses open parentheses x close parentheses open parentheses begin display style fraction numerator a plus b over denominator 2 end fraction end style close parentheses open parentheses begin display style fraction numerator a minus b over denominator 2 end fraction end style close parentheses end fraction close parentheses
equals negative 2 open parentheses fraction numerator a plus b over denominator 2 end fraction close parentheses open parentheses fraction numerator a minus b over denominator 2 end fraction close parentheses limit as x rightwards arrow 0 of open parentheses fraction numerator sin open parentheses begin display style fraction numerator a plus b over denominator 2 end fraction x end style close parentheses sin open parentheses begin display style fraction numerator a minus b over denominator 2 end fraction x end style close parentheses over denominator open parentheses begin display style fraction numerator a plus b over denominator 2 end fraction x end style close parentheses open parentheses begin display style fraction numerator a minus b over denominator 2 end fraction x end style close parentheses end fraction close parentheses
equals negative 2 open parentheses fraction numerator a plus b over denominator 2 end fraction close parentheses open parentheses fraction numerator a minus b over denominator 2 end fraction close parentheses 1 cross times 1
equals open parentheses fraction numerator b squared minus a squared over denominator 2 end fraction close parentheses

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