In the above figure, square is inscribed in a circle. is also a square with points and on the circle and and on side of the bigger square.
Find the ratio of the areas of the bigger square to the smaller square correct to 3 decimal places.
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Construction: Let O be the centre of the circle. Join O A , O E and O F . Let J be a point on side E F such that O J ⊥ E F . O J intersects side A B at I .
Let the side lengths of the larger and smaller square be A and a respectively. Then ( 2 R ) 2 = A 2 + A 2 ⟹ 2 R 2 = A 2 .
We have O E = O F = R , so Δ E O F is isosceles. Hence, O J is also the median to side E F . ⟹ E J = J F = 2 E F = 2 a .
Also, ∠ A I O = 9 0 ∘ . ⟹ A I = I B = 2 A and ∠ I A O = 4 5 ∘ ⟹ A I = I O ⟹ I O = 2 A .
Now, since Δ E J O is right angled at J , applying the Pythagorean Theorem,
E J 2 + J O 2 = O E 2 ⟹ ( 2 a ) 2 + ( I J + I O ) 2 = R 2 ⟹ ( 2 a ) 2 + ( a + 2 A ) 2 = R 2 ⟹ a 2 ( 4 1 ) + a 2 ( 1 + a A ⋅ 2 1 ) 2 = 2 A 2
Dividing throughout by a 2 , we have:
( 4 1 ) + ( 1 + a A ⋅ 2 1 ) 2 = ( a A ) 2 ⋅ 2 1
Let a A = k , then the above equation becomes:
4 1 + ( 1 + 2 k ) 2 = 2 k 2
Solving the above quadratic equation, we have k = 5 or − 1 . We reject − 1 as the ratio of the sides cannot be negative. So, k = 5 ⟹ a A = 5 . Hence, ratio of their areas = a 2 A 2 = ( a A ) 2 = 5 2 = 2 5