the minimum area of triangle formed by tangents to ellipse x 2 /a2+y2/b2 =1 and the coordinate axes is

  1. ab
  2. (asquare+bsquare)/2
  3. (a+b)square/2
  4. (asquare+ab+bsquare)/3

The equation of tangent at acosθ, bsinθ to the ellipse, x2a2+y2b2=1 is given as, xcosθa+ysinθb=1or xasecθ+ybcosecθ=1It meets the coordinate axes at Aasecθ, 0 and B0,bcosecθSo area of the triangle, =12×OA×OB=12×asecθ×bcosecθ=12×absinθcosθ=absin2θNow since sin function has maximum value =1 so Area of triangle= absin2θab

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