The maximum area (in sq. units) of a rectangle having

Question:

The maximum area (in sq. units) of a rectangle having its base on the $\mathrm{x}$-axis and its other two vertices on the parabola, $y=12-x^{2}$ such that the rectangle lies inside the parabola, is :-

  1. $20 \sqrt{2}$

  2. $18 \sqrt{3}$

  3. 32

  4. 36


Correct Option: , 3

Solution:

$f(a)=2 a(12-a)^{2}$

$f^{\prime}(a)=2\left(12-3 a^{2}\right)$

maximum at $\mathrm{a}=2$

maximum area $=\mathrm{f}(2)=32$

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