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Mathematics 13 Online
OpenStudy (shaleiah):

Medal and fan for geometry help.

OpenStudy (shaleiah):

@welshfella

OpenStudy (tkhunny):

Find the area of the base. It's a regular hexagon.

OpenStudy (shaleiah):

The formula is \[\frac{ 3\sqrt{3} }{ 2 }*a^2\] ?

OpenStudy (tkhunny):

Okay, is 'a' 8.7 or 10 or something else?

OpenStudy (shaleiah):

10

OpenStudy (michele_laino):

I think that it is: \[\Large \begin{gathered} base\;area = \frac{{perimeter \times apothem}}{2} = \hfill \\ \hfill \\ = \frac{{\left( {10 \times 6} \right) \times 8.7}}{2} = ...? \hfill \\ \end{gathered} \]

OpenStudy (shaleiah):

261

OpenStudy (michele_laino):

ok! and the requested volume is: \[\Large \begin{gathered} volume = base\;area \times height = \hfill \\ \hfill \\ = 261 \times 7 = ...? \hfill \\ \end{gathered} \]

OpenStudy (shaleiah):

1827

OpenStudy (michele_laino):

that's right!

OpenStudy (shaleiah):

I didn't expect the previous formula to be similar to this figure.

OpenStudy (michele_laino):

yes! Such formulas are very similar each to other at a first sight

OpenStudy (shaleiah):

@Michele_Laino

OpenStudy (michele_laino):

here we have to compute the base area first, in order to do that, we can apply the Eron's formula: the half perimeter of the base triangle, is: \[\Large p = \frac{{10 + 8 + 6}}{2} = ...?\]

OpenStudy (shaleiah):

12

OpenStudy (michele_laino):

correct!

OpenStudy (michele_laino):

so the area of the base triangle, is: \[\Large \begin{gathered} area = \sqrt {p\left( {p - a} \right)\left( {p - b} \right)\left( {p - c} \right)} = \hfill \\ \hfill \\ = \sqrt {12 \times \left( {12 - 10} \right) \times \left( {12 - 8} \right) \times \left( {12 - 6} \right)} = ...? \hfill \\ \end{gathered} \]

OpenStudy (shaleiah):

576

OpenStudy (michele_laino):

ok! we have: \(area= \sqrt 576=24\) now the requested volume is: \[\Large volume = \frac{{24 \times 8}}{3} = ...?\]

OpenStudy (shaleiah):

64

OpenStudy (michele_laino):

that's right!

OpenStudy (michele_laino):

I'm very sorry I have to go out now

OpenStudy (tkhunny):

I never liked esoteric formulas. Just build the thing. One of the six triangles that makes the base: \(\dfrac{1}{2}\cdot (10\;ft)\cdot(8.7\;ft) = 43.5\;ft^{2}\) There are 6 of these: \(43.5\;ft^{2}\cdot 6 = 261\;ft^2\). This is the area of the base. \(261\;ft^{2}\cdot 7\;ft = 1827\;ft^{3}\) This is the volume.

OpenStudy (michele_laino):

here I am

OpenStudy (michele_laino):

that's right, the requested volume is \(64\)

OpenStudy (michele_laino):

the base area can be computed noting that the triangle is a right triangle, so we have: area=\((6 \times 8) /2=24\)

OpenStudy (shaleiah):

alright

OpenStudy (michele_laino):

:)

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