Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[warren]

Not possible, to fit 6 regular triangles around the same vertex you'd take up all 360 degrees, so it'd be flat and thus 2d.

Not possible? whatever happened to the triangular tiling?

[frostshotgg]

That's not 3d.

[warren]

It has to be 3D? Next you will be telling me tilings of the hyperbolic plane don't exist as that is not even 2D as we understand it.

[frostshotgg]

He asked for 3d figures. So yes, it does have to be 3d.

[warren]

He asked for creatures. I know of one such infinitely sided creature.

[frostshotgg]

A slchreaoufnefaoui symbol with 2 numbers is a polyhedron. He asked for {3,6} specifically, which would be a polyhedron made of regular three sided figures (triangles), with 6 of them touching each vertex. Which isn't possible to have and still be a polyhedron.

[ShadowHammer]

"Natalie hits a tennis ball into the air along a parabolic trajectory. Her initial point of contact with the ball is 1 m above the ground. The ball reaches a maximum height of 10 m before falling towards the ground. The ball is again 1 meter above the ground when i is 22 m away from where she hit it.

Write a quadratic function to represent the trajectory of the tennis ball if the origin is on the ground directly below the spot from which the ball was hit."

The answer I got was f(x) = ^-9/₁₂₁ (x-11)² + 10.

Spoiler: How I did the question (click to show/hide)

Quadratic equation vertex form, which is the form we are supposed to be using, is f(x) = a(x - p)² + q, where p and q are the x and y coordinates of the vertex, respectively.

p = 11, because the vertex is halfway between the point of contact and where it is again 1 m off the ground, a distance of 22 m (22/2 = 11).
q = 10, because the maximum height the ball reached was 10 m.
a = (-9/121), after solving for it using the point (0,1), which was a point explicitly stated to be on the graph.

The answer key, however, stated that the correct equation was f(x) = ^-9/₁₂₁ (x-11)² + 9.

Can anyone tell me what I did wrong?

edit: apparently "tab" posts the message.

[Karlito]

Can anyone tell me what I did wrong?

Nothing, the answer key is wrong (happens more frequently than you might think).

[ShadowHammer]

Can anyone tell me what I did wrong?

Nothing, the answer key is wrong (happens more frequently than you might think).

Oh. Okay. That's good, I guess. Thanks for the help!

[Zrk2]

High school (I assume) math textbooks have notoriously shitty answer keys. Used to be my calc class would find at least one or two mistakes in the answer key a week.

[Skyrunner]

edit: apparently "tab" posts the message.

To be exact, tab changes the focus from the text box to the "Post" button, and enter activates it.

[MonkeyHead]

High school (I assume) math textbooks have notoriously shitty answer keys. Used to be my calc class would find at least one or two mistakes in the answer key a week.

On occasion, this is deliberate, so the teacher can work out who is relying on the solutions. I know that one text I occasionally teach from does this.

[anzki4]

I'm stuck on task to present line with function y=-x+2 in (vector) form {p̅ + t v̅ | t ∈ ℝ}. I know the answer; for example {(0,2) + t(1,-5) | t ∈ ℝ}, but the problem is to arrive to this conclusion in a mathematically sound way.

Finding the place vector p̅  is simple enough in itself. For example if y=0, x = 2 and therefore p̅  = (0,2). However getting the direction vector v̅  is posing a bigger problem. I know (well, I'm guessing) I need to somehow derive it from function itself, but I can't seem to find a way to do it. Any ideas or tips?

I'm also sorry for quite possibly butchering various mathematical terms (I study math in Finnish  ).

[da_nang]

Since it's a line, assume you're already at (0,2). Say you want to take one step along the line. Were do you end up and which vector would represent such a step?

[anzki4]

Since it's a line, assume you're already at (0,2). Say you want to take one step along the line. Were do you end up and which vector would represent such a step?

Of course, finding another place vector and using substraction to get the direction vector. Thanks!