[Geometry help] Similar Shapes

[astone788]

I'm not good with all this egg head shit, but it looks similar enough to me. VCAA's explanation (that the law of similar shapes do not apply to trapeziums is 100% bullshit) In the math quest 12 the example they use to teach you similar shapes is a trapezium. So wtf?

[astone788]

you can use scale factor with trapeziums and stuff, but you just gotta make sure they are seperate, and not one of those shape in shape ones like above. same with any other shape besides triangles.

Not true. I had one of those questions that is explained here Geometry HELP!!!

[astone788]

Does anyone know why we can't use K-factor for this question? I really don't want to drive to school and see my teacher just for 1 stupid question. 

[Daenerys Targaryen]

and that is a triangle. cones use the same princples as triangles

[Felicity Wishes]

Does anyone know why we can't use K-factor for this question? I really don't want to drive to school and see my teacher just for 1 stupid question. 

Because they aren't similar. If you compare the corresponding sides, one of the sides has the same value. Stumblebum posted a suggested way of answering it.

[astone788]

Damn. It's hard to make that distinguishment, especially when you're in a hurry. Gotta work on this, but thanks for pointing out that the shapes are NOT similar because  "the side on the left (1m) remains 1 from one shape to the other"

For a shape to be similar all sides must be proportional to the sides of the other. So if 1 side expands, all sides should expand!
Going to write this in great big letters in my bound reference

[StumbleBum]

Damn. It's hard to make that distinguishment, especially when you're in a hurry. Gotta work on this, but thanks for pointing out that the shapes are NOT similar because  "the side on the left (1m) remains 1 from one shape to the other"

For a shape to be similar all sides must be proportional to the sides of the other. So if 1 side expands, all sides should expand!
Going to write this in great big letters in my bound reference

The scale factor only works for shapes that are SIMILAR, trapeziums can be similar, but its just that this one wasn't. You have to just make sure, as you said, that you distinguish which are and aren't similar.

[Stick]

You're all doing it the hard way! Here's a hint: why not just construct two triangles and find the angle made with the horizontal and then use it to find the vertical length?

[StumbleBum]

You're all doing it the hard way! Here's a hint: why not just construct two triangles and find the angle made with the horizontal and then use it to find the vertical length?

Nope, I got D. I didn't even bother with similar triangles, and i reckon that would be the more difficult way. I just made a triangle out of the bottom part and then used tan(angle)= OPP/ADJ to work out angle, and then worked backwards to get the new depth at 8m. Was really quite easy in the end.

Way ahead of you Stick

[Daenerys Targaryen]

Even easier: Make the triangles, then use similar triangles there? 8/11 x 0.8 then +1 to that.

[Conic]

A diagram is anyone's still confused: