If a rectangle with length sqrt(a) units and width sqrt(b)

A right triangle inscribed in a circle must have its hypotenuse as the diameter of the circle. Since a rectangle is made of two right triangles then a rectangle inscribed in a circle must have its diagonal as the diameter of the circle.

Thus \((\sqrt{a})^2+(\sqrt{b})^2=10^2\) --> \(a+b=100\).

Answer: E.

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Hope this helps.
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For a rectangle to be drawn in a circle, the diagonal of the rectangle= diameter of Circle=10
and in a rectangle of side c and d respectively we have c^2+d^2= l^2 where l is the diagonal...

In this case we side as \sqrt{a} and\sqrt{b} so a+b= 100....

Do share the OA
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Here is the thing though, why can't you have rectangles of different side dimensions inscribed in the circle as in my attached image?

Just for kicks, I drew the attached image out with a pen, paper, a circular template and a ruler. I understand that the radius is 5 (so diameter is 10) but if we drew a rectangle with almost no height it would be just slightly longer while being a lot more narrow. The ratio of length to width wouldn't change enough to make them the same area.

EDIT: Thinking about it, it makes a bit more sense. They're testing to see whether you completely understand the concept of a right triangle. In a right triangle (which this is, it's two of them) a^2 + b^2 MUST EQUAL c^2. Drawing it out throws you off. If you inscribe a rectangle in a circle and you change the dimensions of that rectangle while still keeping it inscribed, the change in width will offset the change in height and vice versa. I guess my hand drawn attempt at understanding this was incorrect. In other words:

a^2 + b^2 = c^2
6^2 + 8^2 = 100
36 + 64 = 100

(a-b)^2 + (b+a)^2 = 100 as well.

Simple, yet very tricky.

Bunuel

Is it okay to assume that when we create a hypotenuse for a rectangle we cut it into a 30-60-90 triangle?

Hence \(\sqrt{a} = 5\) and \(\sqrt{b} = 5\sqrt{3}\)?

The diagonal of the rectangle is 2*R = 2*5=10

Applying the Pythagorean Theorem gives=

10^2 = (\(\sqrt{a}\))^2 + (\(\sqrt{b}\))^2

100= a+b

E.
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Diagonal of rectangle is equal to the diameter of circle.

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