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The maximum distance from origin of a point on the curve $$x = a\sin t - b\sin \left( {{{at} \over b}} \right)$$ $$y = a\cos t - b\cos \left( {{{at} \over b}} \right),$$ both $$a,b > 0$$ is

JEE · Math · previous-year question

  1. A.$$a-b$$
  2. B.$$a+b$$correct
  3. C.$$\sqrt {{a^2} + {b^2}} $$
  4. D.$$\sqrt {{a^2} - {b^2}} $$

Answer

B. $$a+b$$

Explanation

Distance of origin from $$\left( {x,y} \right) = \sqrt {{x^2} + {y^2}} $$ $$ = \sqrt {{a^2} + {b^2} - 2ab\cos \left( {t - {{at} \over b}} \right)} ;$$ $$ \le \sqrt {{a^2} + {b^2} + 2ab} $$ $$\left[ {{{\left\{ {\cos \left( {t - {{at} \over b}} \right)} \right\}}_{\min }} = - 1} \right]$$ $$=a+b$$ $$\therefore$$ Maximum distance from origin $$=a+b$$

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