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energetics
The function {x} is defined as the area of a square with diagonal of length x. If x > 0 and {x²} = x², what is the value of x?

A) 1
B) √2
C) √3
D) 2
E) 4

Given: The function {x} is defined as the area of a square with diagonal of length x.

Asked: If x > 0 and {x²} = x², what is the value of x?

Area of a square with side a = a^2
Diagonal of a square with side \(a= a*\sqrt{2}\)

\(If x=a*\sqrt{2}\)
\(Area= x^2/2\)
\({x} = x^2/2\)

\({x^2} = x^4/2 = x^2\)
Since x>0
\(x^2/2 = 1\)
\(x = \sqrt{2}\)

IMO B

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jmecen

This question is just confusing because of the way it's written. All it's saying is that if we take a diagonal of a square with length x² it is equal to the area of the square...

We know that a square is 2 special right triangles with relationship s:s:s√2 between sides and diagonal

So, diagonal x² = s√2 --> s = x²/√2 --> area is s² = (x²/√2)²

[area of square] (x²/√2)² = x² [diagonal of square]

x²/√2 = x

x² = x√2

x² - x√2 = 0

x(x - √2) = 0

x = √2 ... x=0 is not a valid solution because x>0 is given
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energetics
The function {x} is defined as the area of a square with diagonal of length x. If x > 0 and {x²} = x², what is the value of x?

A) 1
B) √2
C) √3
D) 2
E) 4

=> {x} is f(x) = \([x/\sqrt{2}]^2\)
Now substituting the expansion into the question.

\([x/\sqrt{2}]^4 = x^2\)
=> \((x^4)/4 = x^2\)
\(=> x^2 = 2 \\
=> x = \sqrt{2}\)
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\(x^4/2=x^2\)

Is correct equation

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energetics
The function {x} is defined as the area of a square with diagonal of length x. If x > 0 and {x²} = x², what is the value of x?

A) 1
B) √2
C) √3
D) 2
E) 4

Function questions can be confusing so we should start by recognizing the inputs and outputs. For the function, the input is the length of a square’s diagonal, and the output is the area of the square. This means we need a relation that represents a square’s area in terms of the square’s diagonal. We have the relation \(\frac{Diagonal^2}{2} = Area\). So if we input D for the diagonal, we receive \(\frac{D^2}{2}\) as the output. If we input \(x^2\) as {\(x^2\)} suggests, we plug in \(x^2\) for the diagonal to get \(\frac{x^4}{2}\) is the area.

FInally we get \(\frac{x^4}{2} = x^2\), solving that gives \(x = \sqrt{2}\).
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TestPrepUnlimited

So if we input D for the diagonal, we receive \(\frac{D^2}{2}\) as the output.


This is what is got wrong. I mistakenly squared the whole function, instead of just squaring the diagonal value.
Many thanks for clearing the doubt for me.

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