Radius

In classical geometry, the radius of a circle or sphere is a the length of a line segment from its center to its perimeter. The name comes from Latin radius, meaning "ray" but also the spoke of a chariot wheel. The plural of radius can be either radii (from the Latin plural) or the conventional English plural radiuses. The typical abbreviation and mathematic variable name for "radius" is r. By extension, the diameter d is defined as twice the radius:

If an object does not have a center, the term may refer to its circumradius, the radius of its circumscribed circle or circumscribed sphere. In either case, the radius may be more than half the diameter, which is usually defined as the maximum distance between any two points of the figure. The inradius of a geometric figure is usually the radius of the largest circle or sphere contained in it. The inner radius of a ring, tube or other hollow object is the radius of its cavity.

For regular polygons, the radius is the same as its circumradius. The inradius of a regular polygon is also called apothem. In graph theory, the radius of a graph is the minimum over all vertices u of the maximum distance from u to any other vertex of the graph.

Khan Academy

Khan Academy is a non-profit educational organization created in 2006 by educator Salman Khan with the aim of providing a free, world-class education for anyone, anywhere. The organization produces short lectures in the form of YouTube videos. In addition to micro lectures, the organization's website features practice exercises and tools for educators. All resources are available for free to anyone around the world. The main language of the website is English, but the content is also available in other languages.

History

The founder of the organization, Salman Khan, was born in New Orleans, Louisiana, United States to immigrant parents from Bangladesh and India. After earning three degrees from the Massachusetts Institute of Technology (a BS in mathematics, a BS in electrical engineering and computer science, and an MEng in electrical engineering and computer science), he pursued an MBA from Harvard Business School.

In late 2004, Khan began tutoring his cousin Nadia who needed help with math using Yahoo!'s Doodle notepad.When other relatives and friends sought similar help, he decided that it would be more practical to distribute the tutorials on YouTube. The videos' popularity and the testimonials of appreciative students prompted Khan to quit his job in finance as a hedge fund analyst at Connective Capital Management in 2009, and focus on the tutorials (then released under the moniker "Khan Academy") full-time.

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Lyrics list:

lyrics

100% Dundee, Roots

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Ain't Sayin' Nothin' New, Roots

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Adrenaline, Roots

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Act Too.. The Love of My Life, Roots

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Act Fore... The End?, Roots

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A Peace Of Light, Roots

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75 Bars (Black's Reconstruction), Roots

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Diedre Vs. Dice, Roots

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Dear God 2.0, Roots

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Dave Vs. Us, Roots

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Break You Off, Roots

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Here I Come, Roots

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Guns Are Drawn, Roots

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Grits, Roots

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Good Music (Prelude), Roots

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Good Music, Roots

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Glitches, Roots

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Bread & Butter, Roots

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Get Busy, Roots

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Game Theory, Roots

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For The Love Of Money, Roots

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False Media, Roots

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Episodes, Roots

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Dynamite, Roots

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Boom, Roots

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Birthday Girl, Roots

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Duck Down!, Roots

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Double Trouble, Roots

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Don't See Us, Roots

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Don't Say Nuthin', Roots

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Don't Feel Right, Roots

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Doin' It Again, Roots

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Do You Want More?!!!??!, Roots

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Distortion To Static, Roots

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Datskat, Roots

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Criminal, Roots

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Concerto Of The Desperado, Roots

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Complexity, Roots

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Common Dust, Roots

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Clones, Roots

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Clock With No Hands, Roots

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Can't Stop This, Roots

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Baby, Roots

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Atonement, Roots

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Staring At The Rude Boys, Ruts

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Sus, Ruts

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Jah War, Ruts

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In A Rut, Ruts

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Babylon's Burning, Ruts

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West One (shine On Me), Ruts

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100% Dundee

One one one one two
P-P-5-D
Yeah, yeah, P-P-5-D
I'm sayin, yo
Touch this yo, knahmsayin what?
Yo-yo, yo, 100%..
[Black Thought]
Yo! On these seventy-three keys, of ivory and ebony
I swear solemnly that I'll forever rock steadily
People wanna know where Malik? He right next to me
The weaponry, the secret recipe
Hard to peep this, deep shit, shows I eat with
Contaminated thoughts I walk the street with
I bayonnet cassettes and chop beats with
this olympic lyricism you can't, compete with
Globe travellin, throwin your verse like a javelin
Things Fall Apart and MC's unravellin
Backstage whisperin to management like
"change the order, it's no way that we can rock after them"
My man sport the 'fro like _What's Happenin?_
From the latest hi-atus, The Roots back again
Your crew practicin to catch this natural blend
They packages read "care when handlin"
It's all soft shit, batteries not included with
Matter of fact, your whole front's a re-enactment
I blow your ba-tty ass into fragments, P-5-D
The new testament, mic specialist, what?
Yeah
Check it out, yo [3X]
Yo yo, Black Thought, I represent the Fifth Dynasty
Lyrical click, 100% Dundee
[Malik B]
Malik B, I represent the P-5-D
Guerilla click, 100% Dundee
[Black Thought]
Black Thought, I represent the Fifth Dynasty
Lyrical click, 100% Dundee
[Malik B]
Malik B, I represent the P-5-D
Guerilla click, 100% Dundee
The Milli-illitant-tant, 'pon cock, ready to rock
Power out, in the clout, it seems out, all through your block
Posse don't play the cut, but what, you get sheist
Got the personality named trife, ready to heist
Smashin 'graphs, snatch the ice, crush your mental device
Thought twice, shoulda thought once, got played for the dunce
Dialogues I moderate, cool out, we outta state
Just blendin in the great, give me room to ventilate
Most niggaz is fraudulent, the rap seargeant
Bargin, through your regiment, call your president
Hittin all targets cuz it's a cause that's lost
Between the killers when they probably Teddy Ruxpin talk
Droppin tears of steel, two drops up in the bucket
Facin three ? and a cop so yo fuck it
If I get abducted, trapped up in the belly
Wacked up my celly, get known like Dawn Stanley
You know the deally on the daily in the ?
If I sense you got a bend to your kite, then send it up
We press up on your corner with windows they're tinted up
Lay our props face down on the ground and get it up, what?
Face on the ground and get it up
[Black Thought]
Yo yo, Black Thought, I represent the Fifth Dynasty
Lyrical click, 100% Dundee
[Malik B]
Malik B, I represent the P-5-D
Guerilla click, 100% Dundee
[Black Thought]
Black Thought, I represent the Fifth Dynasty
Lyrical click, 100% Dundee
[Malik B]
Malik B, I represent the P-5-D
Guerilla click, 100% Dundee
[Black Thought]
Check it out
While you pose for pictures, I'm the invisible enigma
Down low, scope you off the roof like the fiddler
Cage you up in the vocal booth, you're held prisoner
Watch, while I'm bangin out this hot shit from Sigma
Illa-del-P-A, live without a DJ
And it's been that way, since Sergio Vallente
Yo, The Roots holdin it down, is all you can say
Plus the Black Thought em-cey, professional-lay
Push pen to paper like Chinua Achebe
Thumpin, what was your assumption
I lace your function, make it a Black Thought production
Word up I'm on somethin, stellar hold off course
I'm gone bluntin, travel light and broadcast
via satellite, Illa-Fifth Dynamite
Lyrically calculus in this arithametic hip-hop metropolis
But loyal fiends coppin this hot shit
Yaknahmsayin? Hot shit, word up
Illa-Fifth hot shit y'all
Black Thought, I represent the Fifth Dynasty
Lyrical click, 100% Dundee
[Malik B]
Malik B, I represent the P-5-D
Guerilla click, 100% Dundee
[Black Thought]
Black Thought, I represent the Fifth Dynasty
Lyrical click, 100% Dundee
[Malik B]
Malik B, I represent the P-5-D

photo: AP / Steve Helber