Maths Without Number.

Geometry Level 3

The picture shows 3 quadrilateral and one circle. -All the quadrilateral are square. -All the orange dot are midpoint of its respective square. -The side of the largest square is q. -Given the area of shaded region (Green) is (3q^2)/[(3L^2) +4].

Use π = ­22/7­ , find the value of L.


The answer is 6.

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3 solutions

Chew-Seong Cheong
Dec 15, 2014

Let the areas of the smallest square and the second smallest square be A 1 A_1 and A 2 A_2 respectively. It is noted that A 1 = 1 2 A 2 A_1 = \frac {1}{2} A_2 . Any the calculations are as follows:

A 1 = A 2 4 × \quad A_1 = A_2 - 4 \times the area of corner triangle

= ( q 2 ) 2 4 ( 1 2 ) ( q 4 ) 2 = ( 1 4 1 8 ) q 2 = 1 8 q 2 \quad \quad \quad = \left( \dfrac {q}{2} \right)^2 - 4 \left( \dfrac {1} {2} \right) \left( \dfrac {q}{4} \right)^2 = \left( \dfrac {1}{4} - \dfrac {1}{8} \right) q^2 = \frac {1}{8} q^2

The radius of the circle, r = 1 2 ( 1 4 ) ( 2 ) q = 2 8 q r = \frac {1}{2} \left( \frac {1}{4} \right) \left( \sqrt {2} \right) q = \frac {\sqrt{2} } {8} q

The area of the shaded region,

A = A 1 π r 2 = 1 8 q 2 22 7 ( 2 8 q ) 2 = ( 1 8 11 112 ) q 2 = ( 14 11 112 ) q 2 = 3 q 2 112 A = A_1 - \pi r^2 = \frac {1}{8} q^2 - \frac {22}{7} \left( \frac {\sqrt{2} } {8} q \right)^2 = \left( \frac {1}{8} -\frac {11 } {112} \right) q^2 = \left( \frac {14 - 11 } {112} \right) q^2 = \dfrac {3q^2 } {112}

3 L 2 + 4 = 112 L = 112 4 3 = 108 3 = 36 = 6 \Rightarrow 3L^2 + 4 = 112\quad \Rightarrow L = \sqrt {\dfrac {112-4}{3}} = \sqrt {\dfrac {108}{3}} = \sqrt {36} = \boxed {6}

Hitoshi Yamamoto
Dec 15, 2014

(3q^2) / ( 3L^2 + 4) = (q^2)/8 - (pi.q^2) / (32)

pi = 22/7

(3q^2) / ( 3L^2 + 4) = (3.q^2) / (8.14)

3L^2 + 4 = 14*8

3L^2 = 112 - 4

L^2 = 108/3

L = 6

Ganesh Ayyappan
Dec 15, 2014

i tink this problem is overrated .... it shud hav been a level 2 problem for 55 points

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