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Question Number 20194 by ajfour last updated on 23/Aug/17
A plane is drawn through the   midpoint of a diagonal of a cube  perpendicular to the diagonal.  Determine the area of the figure  resulting from the section of the  cube cut by this plane if the edge  of the cube is equal to a.
$${A}\:{plane}\:{is}\:{drawn}\:{through}\:{the}\: \\ $$$${midpoint}\:{of}\:{a}\:{diagonal}\:{of}\:{a}\:{cube} \\ $$$${perpendicular}\:{to}\:{the}\:{diagonal}. \\ $$$${Determine}\:{the}\:{area}\:{of}\:{the}\:{figure} \\ $$$${resulting}\:{from}\:{the}\:{section}\:{of}\:{the} \\ $$$${cube}\:{cut}\:{by}\:{this}\:{plane}\:{if}\:{the}\:{edge} \\ $$$${of}\:{the}\:{cube}\:{is}\:{equal}\:{to}\:\boldsymbol{{a}}. \\ $$
Commented by ajfour last updated on 24/Aug/17
thank you Sir.
$${thank}\:{you}\:{Sir}. \\ $$
Commented by mrW1 last updated on 24/Aug/17
the section is a regular hexagon with  side length b=(√2)(a/2)=a/(√2)  A_S =((3(√3))/2)b^2 =((3(√3))/2)×(a^2 /2)=((3(√3))/4)a^2
$$\mathrm{the}\:\mathrm{section}\:\mathrm{is}\:\mathrm{a}\:\mathrm{regular}\:\mathrm{hexagon}\:\mathrm{with} \\ $$$$\mathrm{side}\:\mathrm{length}\:\mathrm{b}=\sqrt{\mathrm{2}}\left(\mathrm{a}/\mathrm{2}\right)=\mathrm{a}/\sqrt{\mathrm{2}} \\ $$$$\mathrm{A}_{\mathrm{S}} =\frac{\mathrm{3}\sqrt{\mathrm{3}}}{\mathrm{2}}\mathrm{b}^{\mathrm{2}} =\frac{\mathrm{3}\sqrt{\mathrm{3}}}{\mathrm{2}}×\frac{\mathrm{a}^{\mathrm{2}} }{\mathrm{2}}=\frac{\mathrm{3}\sqrt{\mathrm{3}}}{\mathrm{4}}\mathrm{a}^{\mathrm{2}} \\ $$
Commented by mrW1 last updated on 24/Aug/17
Commented by Einstein Newton last updated on 24/Aug/17
Does it available on internet?
$$\mathrm{Does}\:\mathrm{it}\:\mathrm{available}\:\mathrm{on}\:\mathrm{internet}? \\ $$
Commented by ajfour last updated on 24/Aug/17
i dont know, but less chance.
$${i}\:{dont}\:{know},\:{but}\:{less}\:{chance}. \\ $$

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