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Find the volume of the cuboid in the form $a\sqrt{b} \text{ cm}^3$, where $a, b \in \mathbb{N}$. - Leaving Cert Mathematics - Question 3(a) - 2021

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Question 3(a)

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Find the volume of the cuboid in the form $a\sqrt{b} \text{ cm}^3$, where $a, b \in \mathbb{N}$.

Worked Solution & Example Answer:Find the volume of the cuboid in the form $a\sqrt{b} \text{ cm}^3$, where $a, b \in \mathbb{N}$. - Leaving Cert Mathematics - Question 3(a) - 2021

Step 1

Identify the relationships between dimensions

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Answer

The cuboid has dimensions xx, yy, and zz cm. We can use the areas given to establish relationships:

  1. From the area of the face with dimensions xx and zz:
    xz=22xz = 2\sqrt{2}
  2. From the area of the face with dimensions yy and zz:
    yz=86yz = 8\sqrt{6}
  3. From the area of the face with dimensions xx and yy:
    xy=43xy = 4\sqrt{3}

Step 2

Express $y$ in terms of $x$ and $z$

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Answer

From the equation xz=22xz = 2\sqrt{2}, we can express zz in terms of xx as follows:

z=22xz = \frac{2\sqrt{2}}{x}

Substituting into the second equation, we can express yy in terms of xx:

y(22x)=86y=86x22=43xy \left(\frac{2\sqrt{2}}{x}\right) = 8\sqrt{6} \Rightarrow y = \frac{8\sqrt{6}x}{2\sqrt{2}} = 4\sqrt{3}x

Step 3

Calculate volume $V$

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Answer

Now, substituting yy and zz into the formula for volume V=xyzV = xyz:

V=x(43x)(22x)=86xV = x(4\sqrt{3}x)\left(\frac{2\sqrt{2}}{x}\right) = 8\sqrt{6}x

Now substituting x=1x = 1 (since we have used x2=1x^2 = 1 from other calculations):

V=86 cm3V = 8\sqrt{6} \text{ cm}^3

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