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)

Guest Aug 29, 2018

#1**+2 **

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!

tertre
Aug 29, 2018

#2**+2 **

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.

tertre
Aug 29, 2018

#3**+2 **

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.

tertre
Aug 29, 2018

#8**+1 **

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

CPhill
Aug 29, 2018

#9**+1 **

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

CPhill
Aug 29, 2018