Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

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greg1313 wrote:

iamaditya, it has been four and a half months since your last reply to bobbym, who has since died.

The answer to # 15 is log(12).

That is news to me. I didn't know bobbym, but he helpfully replied to some of my posts here. RIP.

Geogebra is pretty nice.

**numquester**- Replies: 1

Over the last year I have picked up a handful of math books, looking to better my understanding of math fundamentals before going further. One of those books which I have found to be excellent in clarifying concepts of fundamental topics is, *Yes, But Why? Teaching for understanding in mathematics, Ed Southall*.

This book is obviously aimed at teachers, but as an independent learner I have found it to be an excellent resource for getting a solid birdseye view of various topics and how things work. I only wish that it existed long ago (it was released earlier this year), as I have wasted alot of time over the years digging through various resources, often running in circles and hitting walls or becoming bored to death. The book begins at arithmetic and graduates through topics in algebra, geometry, and ends with fundamentals in trigonometry.

What I like about it:

- It gets right to the point of concepts without burrying the reader in a bunch of fluff or too much detail from the getgo.

- It doesn't focus on procedures over concepts.

- It makes good connections from one topic to the next, not leaving gaping holes in understanding.

- Reading it has been a series of 'Ah, ha' moments without the brickwalls of so many other resources.

- It makes good use of graphics for explaining concepts; doesn't include graphics for the sake of dressing things up.

- It isn't stodgy in style; it is very conversational in style. It is an educational and fun read at the same time.

- It makes many mentions of where math terms come from and how they relate to the topic at hand, along with other historical bits.

- It is (along with many articles at MathisFun) what I feel in many ways, how math should be taught.

I am not associated with this book in any way. Just sharing a resource that I have found to be exceptional among math books as an adult self-learner relearning math fundamentals. This book, along with MathisFun, Geogebra, and exploring using a compass and rule (because working with my hands is often more satisfying) have been time well spent. I am finding myself to be a visual learner, where numbers often are only added precision in application of concepts.

Answered by a member at the Geogebra forum. Degrees must be indicated within the function. The angle unit setting in Geogebra's preferences is for the display of graphics only; not for setting input value units of those functions which expect angle values as the input, such as sin(), cos(), tan().

The degree symbol must be entered following the degree number. A popup window with symbols can be brought up by clicking the button in the far left of the input box, where the degree symbol can be found at the bottom of the window (in Geogebra 5).

I think my point of confusion stemmed from the angle unit setting. When setting the angle unit in a calculator, any functions which expect angle values will use that angle unit setting, where in Geogebra, only graphing is affected by the angle unit setting. Also in Geogebra, there is nothing in the preferences window stating that the angle unit setting only affects graphing.

**numquester**- Replies: 2

To present this as simply as possible, say I have a right triangle with sides: adjacent = 0.71; opposite = 0.71; hypotenuse = 1. The angle theta is 45 degrees. When I enter in the input box, *sin(45)* , I get 0.85, which is obviously not the sine of 45 degrees.

Am I doing something wrong here? In case it is relevant, I am using Geogebra 5 with the angle unit set to degrees.

Obviously, you want 1/2 of 3/4 of old fashioned oats for making 1/2 of the recipe. Maybe what it isn't so obvious is that division by 2 gives the same result as multiplication by 1/2:

To make sense of the above, remember that any number can be rewritten as the number over 1...

...and to get half of *something*, we have to divide it by 2...

...which can be rewritten as a multiplication...

And so...

Bob, that is a very clear explanation. Thanks for taking the time.

**numquester**- Replies: 2

I came across a video in which the author explains visually how to arrive at the quadratic formula, except he skips some steps.

Here is the video: https://www.youtube.com/watch?v=EBbtoFMJvFc

I follow it up to this point, where some steps are skipped: https://www.youtube.com/watch?v=EBbtoFMJvFc&t=7m45s

In the video, the right side of the equation goes from:

To:

So I think that I can rewrite the first example like this:

But I don't see how the ** a** can be moved to the numerator. Or maybe I'm approaching it all wrong.

By the way, I really like this approach to explaining math. I never understood what 'completeing the square' actually means until I saw this video. It seems right at home with so many of the nice explanations here at Math is Fun.

Side note: I really appreciate the LaTeX integration in the forum. This is nice!

Agnishom wrote:

I like writing too. Have you seen my notes?

They could be hidng in a piano, or other such place.

Agnishom wrote:

Ghoulash?

A main ingredient in ghoul gravy, which gained popularity shortly after the development of the modern crematory.

**numquester**- Replies: 66

I assume that it is an abbreviation for, <something> math.

Thanks.

**numquester**- Replies: 3

I'm relearning algebra after some years of being away from school, and I'm learning to use Geogrebra. At the moment I'm plotting some lines to get a sense of what elementary functions look like on a grid. I never really got a good sense of this when I was in school.

So I have:

f(x) = x , which gives a diaganol line.

f(x) = -x , which gives a mirror of the above diagonal line (Is there a math term for this?).

f(x) = 0x , which gives a horizontal line.

How would I plot a vertical line? The closest that I have found is:

f(x) = 10^(100)x

**numquester**- Replies: 3

Great site. I have been visiting here sporadically over a couple of years, and it is always a good experience. I guess it is about time that I joined the forum. Thanks to everyone who contributes to the site and discussion on the forum.

About myself: I am an adult who never learned much math outside of basic algebra. I am going back and relearning algebra, looking at going much further. My interests in math stem from interests in music, electronics, programming, carpentry, and other areas. And I am coming around to finding out that math is interesting in it's own right.

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