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# Help!

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9 Hi,

Sorry. I am having a very difficult time with surface area. I tried to work the last two out but I am not sure if they are correct or not*. The other three I can't seem to figure out at all. Please help! Thank you!

*(sorry for my crappy writing)

Aug 29, 2018

#1
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Last one: There are 6 faces, I think, wait, yes! So, the area of the first face, 2nd face: 2(20*10)=2(200)=400yd^2

Area of the 3rd face, 4th face: 2(20*20)=2(400)=800yd^2

Ares of the 5th face, and 6th face: 2(20*10)=2*200=400yd^2.

Thus, the surafce area is 400+400+800=1600yd^2. You're correct!

Aug 29, 2018
#2
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5th one: Two trapezoids! No! Area of a trapezoid: 2(51.85)- use the formula=103.7 mi^2.

Rectangles: 2(14*7)=196 mi^2

Bottom rectangle: 5*14=70 mi^2

Top rectangle: 168 mi^2

So, 103.7+196+70+168=537.7? I might be wrong.

Aug 29, 2018
#6
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You are correct,  tertre !!   CPhill  Aug 29, 2018
#3
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1st one: Base, which is a rectangle: 18*20=360mi^2

2*(1/2*20*14.2) and 2*(1/2*18*14.9)=20*14.2+18*14.9=284+268.2=552.2mi^2

So, 360mi^2+552.2mi^2=912.2mi^2.

Aug 29, 2018
#4
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Thank you so much!! I've been having a difficult time with these and I appreciate your help!

Guest Aug 29, 2018
#5
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No problem! I am always happy to help!

tertre  Aug 29, 2018
#7
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Nice job,  tertre.....!!!   Aug 29, 2018
#8
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Third one  (on top right)

We have a  triangular  pyramid

The sides are 3 congruent triangles  with bases of 9 cm  and heights of 19.2 cm

So...their  total area  is  (3)(1/2) (9) (19.2)   = 259.2 cm^2

The base is a triangle with a base  of  9cm  and a height of 7.8 cm

Its  area is  (1/2) (9)(7.8)  = 35.1 cm^2

So.....the total surface area  is   259.2  + 35.1   =  294.3 cm^2   Aug 29, 2018
#9
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Middle one at top

We have a triangular prism

The  top/bottom are congruent triangles  with base = 15 in  and height of 7.7 in

So the total area of top/bottom  is    15  * 7.7  = 115.5 in^2

The sides are rectangles with height  of  8 in and widths of  ( 15,15 and 8  in)

So the side area  is     8 [ 15 + 15 + 8 ]  = 8 [ 38  ] =  304 in^2

So..the total surface area is   115.5  + 304  =  419.5 in^2   Aug 29, 2018