[Geometry help] Similar Shapes

[astone788]

Yo I need help with this question:
The swimming pool is 11 metres long and the depth increases uniformly from 1 metre at the shallow end to 1.8 metres at the deep end.

In my experience, two fiqures are similar if they are the same shape and the corresponding dimentions are in the same ratio.Therefore, the sides of one similar shape are all proportional to the sides of the other, so K-factor can be used to calculate the unknown lengths. But apparantly this rule doesnt apply to trapeziums. Can anyone please clarify?

[Daenerys Targaryen]

That is true. you gotta use trianges with this one. make triangles from the bottom. then add 1m to the result

[astone788]

SO the rule of similar shapes applies to EVERY shape except for trapeziums??? OK that makes a lot of sense... 

[Felicity Wishes]

Why doesn't it work for trapeziums?

[astone788]

I have no idea shapes were racist??? Why doesnt the laws of similar shapes apply to ALL shapes???

[Conic]

They are congruent, not similar.

[Felicity Wishes]

I got B. Hoping someone else did as well.

[StumbleBum]

I got B. Hoping someone else did as well.

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.

[Felicity Wishes]

I got B. Hoping someone else did as well.

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.

You were right. *forever wishes I had your math ability*

[StumbleBum]

You were right. *forever wishes I had your math ability*

Pun intended? Also when did you change your name..?

[Felicity Wishes]

You were right. *forever wishes I had your math ability*

Pun intended? Also when did you change your name..?

No pun.
A sneaky mod changed it.

[astone788]

So next time I see a trapezium, I have a new gameplan. Don't use K-factor!!!

[Daenerys Targaryen]

I think i have come up with a reasoning, but dont take it as 100%
with this example, it doesnt work because not all sides grow in proportion to each other. that side on the left (1m) remains one from one shape to the other. in other words getting from small to big, we're streching if you like. although angles and such are all the same, the shape is growing by a factor.
not sure if this is clear enough but best way i can explain it.

[Felicity Wishes]

I think i have come up with a reasoning, but dont take it as 100%
with this example, it doesnt work because not all sides grow in proportion to each other. that side on the left (1m) remains one from one shape to the other. in other words getting from small to big, we're streching if you like. although angles and such are all the same, the shape is growing by a factor.
not sure if this is clear enough but best way i can explain it.

True. Which means they aren't similar.

[Daenerys Targaryen]

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.