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Mathematics 15 Online
OpenStudy (anonymous):

Find the lateral area the regular pyramid. Need help to solve it

OpenStudy (anonymous):

OpenStudy (jdoe0001):

would you say that's about right for the BOTTOM of the hexagonal pyramid?

OpenStudy (jdoe0001):

OpenStudy (anonymous):

5 times 6 times 6

OpenStudy (anonymous):

180?

OpenStudy (anonymous):

yes

OpenStudy (jdoe0001):

ok, so, what would be "green" line? using the pythagorean theorem

OpenStudy (anonymous):

5 so the answer is 180

OpenStudy (anonymous):

would i set it up as 6^2 + 6^2 = x ?

OpenStudy (jdoe0001):

well, $$ c^2= a^2+b^2\\ \text{what you need is "b",solve for "b"}\\ b^2 = c^2-a^2 \implies b = \sqrt{c^2-a^2} $$

OpenStudy (jdoe0001):

from the right-angle, you have the hypotenuse, or "c", which the longest side, 6 the adjacent, or the shorter given side, or "a" which is 3

OpenStudy (anonymous):

ok so b^2 = sqrt7 ?

OpenStudy (jdoe0001):

yes

OpenStudy (jdoe0001):

or \(\sqrt{27} = 3\sqrt{3}\)

OpenStudy (jdoe0001):

so, now let's find the lateral sides "nose", or the so-called "slant-height"

OpenStudy (jdoe0001):

OpenStudy (jdoe0001):

keep in mind that, though slanted for perspective, the "yellow" triangle is a right-triangle so, using the known values, 8 and \(3\sqrt{3}\), use the pythagorean theorem to get the "longest" side, the one going to the top of the pyramid

OpenStudy (jdoe0001):

the "longest" side will be the hypotenuse the opposite side, that is "b" is 8 the adjacent side, that is "a" is \(3\sqrt{3} $$ c^2= a^2+b^2\\ 3\sqrt{3} = \color{blue}{\sqrt{27}}\\ c^2 = (\color{blue}{\sqrt{27}})^2+(8)^2\\ c = \sqrt{(\color{blue}{\sqrt{27}})^2+(8)^2}\\ $$

OpenStudy (jdoe0001):

hmmm

OpenStudy (jdoe0001):

hehe my bad :)

OpenStudy (jdoe0001):

the "longest" side will be the hypotenuse the opposite side, that is "b" is 8 the adjacent side, that is "a" is \(3\sqrt{3}\) $$ c^2= a^2+b^2\\ 3\sqrt{3} = \color{blue}{\sqrt{27}}\\ c^2 = (\color{blue}{\sqrt{27}})^2+(8)^2\\ c = \sqrt{(\color{blue}{\sqrt{27}})^2+(8)^2}\\ $$

OpenStudy (anonymous):

c= 729 + 64 which = 793. So i then squareroot 793 ?

OpenStudy (jdoe0001):

well, \((\sqrt{NUMBER})^2 = NUMBER\)

OpenStudy (jdoe0001):

so \(c = \sqrt{(\color{blue}{\sqrt{27}})^2+(8)^2} = \sqrt{27+64} = \sqrt{91}\)

OpenStudy (jdoe0001):

|dw:1371684071360:dw| so, now you just need to find the area of that triangle, that one face area of a triangle = \(\large \cfrac{1}{2} \times base \times height\) you get that area, the pyramid is a hexagon, so there are 6 of those triangles, add them together, and that's your Pyramid Lateral Area

OpenStudy (anonymous):

180/2=90 which is final answer

OpenStudy (anonymous):

base= 6 and height= sqrt 91 right?

OpenStudy (jdoe0001):

yes

OpenStudy (anonymous):

the area is sqrt 273?

OpenStudy (jdoe0001):

$$ \cfrac{1}{2}\times 6 \times \sqrt{91} = 28.6\\ 28.6\times 6 = 171.6 $$

OpenStudy (anonymous):

so i add all 6 and get 1,029.6

OpenStudy (jdoe0001):

ahemm well, 1 triangle, that is 1 side, 1 lateral, is 28.6 in Area so 28.6 + 28.6 + 28.6 + 28.6 + 28.6 + 28.6 = 171.6

OpenStudy (anonymous):

Oh. so the lateral area is 171.6?

OpenStudy (jdoe0001):

yes, for a pyramid, the "laterals" or the "sides" area, that is, not including its bottom/base is the area of all her triangles around her

OpenStudy (jdoe0001):

this one is a HEXAgon, so 6 sides, so 6 triangles, so you add them up

OpenStudy (anonymous):

Thank you so much!!!

OpenStudy (jdoe0001):

yw

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