InterviewSolution
Saved Bookmarks
| 1. |
If the normal at any point P on ellipse `(x^(2))/(a^(2))+(y^(2))/(b^(2)) =1` meets the auxiliary circle at Q and R such that `/_QOR = 90^(@)` where O is centre of ellipse, thenA. `a^(4) +2b^(3) ge 3a^(2)b^(2)`B. `a^(4) +2b^(4) ge 5a^(2)b^(2)+2a^(3)b`C. `a^(4)+2b^(4) ge 3a^(2)b^(2)+ab`D. None of these |
|
Answer» Correct Answer - B Normal at `P(a cos theta, b sin theta)` is `ax sec theta - by cosec theta = a^(2) -b^(2)` Homogenising with auxilliary circle `x^(2) + y^(2) = a^(2)` `x^(2) + y^(2) = (a)^(2) ((ax sec theta - by cosec theta)^(2))/((a^(2)-b^(2))^(2))` `:.` For `/_QOR = 90^(@)` Coefficient of `x^(2)+` Coefficient of `y^(2) =0` `1- (a^(4)sec^(4)theta)/((a^(2)-b^(2))^(2)) + 1-(a^(2)b^(2)cosec^(2)theta)/((a^(2)-b^(2))^(2)) =0` `a^(4) - 5a^(2)b^(2) + 2b^(4) = a^(4) tan^(2) theta + a^(2)b^(2) cot^(2) theta` `:. AM ge GM` `a^(4) - 5a^(2)b^(2)+2b^(4) ge 2a^(3)b` |
|