Volume of a frustum

[Abbeegale]

Hey, could someone please help me out with question 14? I'm unsure of what the perpendicular height would be on the frustum. Thank you!

An image of the question is right here:
 

[jakesilove]

Hey, could someone please help me out with question 14? I'm unsure of what the perpendicular height would be on the frustum. Thank you!

An image of the question is right here:
 (Image removed from quote.)

Hey! Here, you want to be looking at similar triangles. In the centre of the square based pyramid, vertically, you can imagine that the outline is just a triangle, right? The total vertical height of the triangle is 180cm, the bottom side is 200cm, and the other two sides are equal (you could work out their length using Pythag if you wanted). Now, draw a line cutting the triangle, parallel to the base, somewhere near the top. This indicates the section of the triangle you are going to 'cut off'. The length of the smaller line, parallel to the base, is going to be 100cm. Now, we can use similar triangles to work out the height! We know that the big triangle is similar to the small triangle (AAA), and so we can use the ratio of lengths





So, we have the new perpendicular height! Kinda makes sense? Hard to explain without a diagram, and I can't draw one right now. If you're still confused, happy to explain further in the morning!