• David Bai on April 20, 2017 at 1:12 am

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 on April 20, 2017 at 1:13 am

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?

1. 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 on February 24, 2019 at 8:42 pm

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

• Super on February 24, 2019 at 8:44 pm

It’s actually surface area=4pi r^2
Volume is 4/3pi r^3

• David Bai on April 29, 2017 at 10:45 pm

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?

1. 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 on April 30, 2017 at 4:10 am

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, …

1. 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 on April 30, 2017 at 3:56 pm

Ok thanks