00:01
In this question we need to inscribe a rectangle in the ellipse.
00:05
So the equation of ellipse is given to us which is x squared divided by 4 plus y square is equals to 1 and y is greater than 0.
00:17
And we also have to maximize the area of the rectangle.
00:22
So we will let the length of rectangle.
00:32
Be equals to l and width of rectangle be equals to w.
00:46
So area of the rectangle will be equal to l multiplied by w which is length multiplied by the width so here we put length as 2x multiplied by the width which is 2 y so it will be 4 xy and we have to maximize the area.
01:11
So we will make y as a subject from the equation of the ellipse.
01:19
So a which is the area will be equals to 4 x multiplied by if we will make y from the subject of the equation of the ellipse.
01:31
So it will be 1 minus x squared divided by 4 inside the root.
01:38
So if we will simplify it, we will get 2x square root of 4 minus x square.
01:48
So this is a function of the area.
01:50
So we will put a dash of x is equal to 0 for finding the critical points.
01:58
So on differentiating the function, we will get.
02:04
2 square root of 4 minus x squared plus 2x multiplied by minus 2x divided by square 2 2 minus x squared and 8 it will be 2 so it should be equals to 0 so from here on simplifying it we will get 8 minus 4 x square divided by square 2 root of 4 minus x square is must be equals to 0 so from here we will get the well value of x will be equals to square root of 2.
02:37
So now we will double differentiate it to find whether it is maximum or minimum...