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A square with sides of length 10 units is shown in the diagram - Junior Cycle Mathematics - Question 7 - 2015

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A square with sides of length 10 units is shown in the diagram. A point A is chosen on a diagonal of the square, and two shaded squares are constructed as shown. By ... show full transcript

Worked Solution & Example Answer:A square with sides of length 10 units is shown in the diagram - Junior Cycle Mathematics - Question 7 - 2015

Step 1

Find the minimum possible value of the total area of the two shaded squares.

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Answer

Let the side of the square to the left of point A be denoted as AA, and the side of the square to the right be (10A)(10 - A). Then, the total area of the shaded squares can be expressed as:

extArea=A2+(10A)2 ext{Area} = A^2 + (10 - A)^2

Expanding this gives:

=A2+(10020A+A2)= A^2 + (100 - 20A + A^2) =2A220A+100= 2A^2 - 20A + 100

To find the minimum area, we take the derivative of the area function and set it to zero:

rac{d( ext{Area})}{dA} = 4A - 20 = 0

Solving for A yields:

A=5A = 5

Substituting A=5A = 5 back into the area equation provides:

extArea=2(5)220(5)+100=50 ext{Area} = 2(5)^2 - 20(5) + 100 = 50

Thus, the minimum possible value of the total area of the two shaded squares is 50.

Step 2

Show that the value of the total area of the two shaded squares is equal to d².

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Answer

To prove that the area of the two shaded squares is equal to d2d^2, we first apply the Pythagorean theorem. In the right triangle formed by the diagonal d, we have:

d2=A2+(10A)2d^2 = A^2 + (10 - A)^2

Expanding the right side results in:

d2=A2+(10020A+A2)d^2 = A^2 + (100 - 20A + A^2) =2A220A+100= 2A^2 - 20A + 100

This matches the area expression we derived in part (a). Thus, we can conclude that:

The total area of the two shaded squares is indeed equal to d².

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