Why are these called radicals? And I have another question completely unrelated, why are sine, cosine, and tangent called those names? Someone told me that sine represents sinus in Greek, which means curve (and of course co-sine is the opposite), but why? And what do these trigonometric functions stand for, for example sin(9), is that nine time something? Thank you but I haven’t seen the rest of the videos so I don’t know if my questions are already explained.

And I have another question. Now there are commonly surface area or volume questions on number sense tests, so how do you find those, lets say, of a sphere? Can you make a video or explain it to me? And also, how do you find the area of a square with its diagonal, or the other way around?

I don’t know what grade you are in but if your seventh grade I am teaching some of line summer classes and I would be covering a lot of what you are asking. Let me know if you are interested.
To answer your question is quite a lot to teach but the area of a square is diagonal squared divided by 2.
Surface area of a sphere is 4/3pi r to third power but it an estimator so the pi and divide by 3 cancel making it basically 4 R to the third

I think I’ll be going to the classes, what calculator do you prefer I get, and is there a qualifier to go to the level 2 classes? And I’m in seventh grade how did you guess?

Thanks, Ill be applying for all five classes, but do i have to have that calculator, i have a casio fx300ESplus, can i use that? And what will you be going over in you lessons, will everyone be in the same video? And your first numbersense lessons starts while im still in school, …

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## David Bai

April 20, 2017 at 1:12 am (UTC 0) Link to this comment

Why are these called radicals? And I have another question completely unrelated, why are sine, cosine, and tangent called those names? Someone told me that sine represents sinus in Greek, which means curve (and of course co-sine is the opposite), but why? And what do these trigonometric functions stand for, for example sin(9), is that nine time something? Thank you but I haven’t seen the rest of the videos so I don’t know if my questions are already explained.

## David Bai

April 20, 2017 at 1:13 am (UTC 0) Link to this comment

And I have another question. Now there are commonly surface area or volume questions on number sense tests, so how do you find those, lets say, of a sphere? Can you make a video or explain it to me? And also, how do you find the area of a square with its diagonal, or the other way around?

## anthony gillespey

April 20, 2017 at 1:57 am (UTC 0) Link to this comment

I don’t know what grade you are in but if your seventh grade I am teaching some of line summer classes and I would be covering a lot of what you are asking. Let me know if you are interested.

To answer your question is quite a lot to teach but the area of a square is diagonal squared divided by 2.

Surface area of a sphere is 4/3pi r to third power but it an estimator so the pi and divide by 3 cancel making it basically 4 R to the third

## Super

February 24, 2019 at 8:42 pm (UTC 0) Link to this comment

The surface area of a sphere is 4pi r^2, and volume is 4/3pi r^3

## Super

February 24, 2019 at 8:44 pm (UTC 0) Link to this comment

It’s actually surface area=4pi r^2

Volume is 4/3pi r^3

## David Bai

April 29, 2017 at 10:45 pm (UTC 0) Link to this comment

I think I’ll be going to the classes, what calculator do you prefer I get, and is there a qualifier to go to the level 2 classes? And I’m in seventh grade how did you guess?

## anthony gillespey

April 30, 2017 at 12:04 am (UTC 0) Link to this comment

The calculator you need to be any good at all at is an HP35S https://www.amazon.com/HP-35S-Programmable-Scientific-Calculator/dp/B004A0XHH4/ref=sr_1_1?ie=UTF8&qid=1493510617&sr=8-1&keywords=hp+35s. If you have never used one before I would suggest you sign up for level 1 and 2. You can save 25 dollars and learn how to use the calculator along with how to do the hard word problems.

## David Bai

April 30, 2017 at 4:10 am (UTC 0) Link to this comment

Thanks, Ill be applying for all five classes, but do i have to have that calculator, i have a casio fx300ESplus, can i use that? And what will you be going over in you lessons, will everyone be in the same video? And your first numbersense lessons starts while im still in school, …

## anthony gillespey

April 30, 2017 at 5:32 am (UTC 0) Link to this comment

Yeah you will want the 35s its an rpn calculator built for speed.

Each lesson will be video taped and shared with classmembers so you won’t miss anything.

## David Bai

April 30, 2017 at 3:56 pm (UTC 0) Link to this comment

Ok thanks