Another SA of Pyramid Question, please can you check where my mistake/s are: (1 Viewer)

[kpad5991]

SA front = 1/2 x 12 x 5 = 30 cm^2

SA bottom = 1/2 x 9 x 12 = 54 cm^2

SA back = 1/2 x 15 x 5 = 37.5 cm^2 used Pythagoras to get 15 cm

SARHS = 1/2 x 9 x root 148.75 = 54.9 cm^2 used Pythagoras h^2 = 13^2 - 4.5^2, h = root 148.75

TOTAL SA = 176.4 cm^2

However the answer says 180 cm^2 (what am I doing wrong?)

 

[Lith_30]

You made a mistake in calculating the area of the top triangle. If you look at the pyramid from a birds eye view, the triangle at the very top is a right angle triangle as its vertices bend to the same degree as the triangle at the base.

 

[kpad5991]

You made a mistake in calculating the area of the top triangle. If you look at the pyramid from a birds eye view, the triangle at the very top is a right angle triangle as its vertices bend to the same degree as the triangle at the base.

Thank you, but that will still be an SA of 175.5cm^2 the answer says 180 cm^2 (to one decimal place). So not too sure where the 4.5 cm^2 comes from

 

[Lith_30]

Thank you, but that will still be an SA of 175.5cm^2 the answer says 180 cm^2 (to one decimal place). So not too sure where the 4.5 cm^2 comes from

I think I might of explained it badly, the height of the triangle at the top would be the hypotenuse of the triangle at the front. Since they are both right angle triangles.

find the height of the top triangle

the area of the top triangle is 58.5cm^2

Add all the other areas up and the answer should be 180cm^2

 

[kpad5991]

I think I might of explained it badly, the height of the triangle at the top would be the hypotenuse of the triangle at the front. Since they are both right angle triangles.

find the height of the top triangle

the area of the top triangle is 58.5cm^2

Add all the other areas up and the answer should be 180cm^2

Thank you