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From Wikipedia

Internal and external angle

In geometry, an interior angle (or internal angle) is an angle formed by two sides of a polygon that share an endpoint. For a simple, convex or concave polygon, this angle will be an angle on the 'inner side' of the polygon. A polygon has exactly one internal angle per vertex.

If every internal angle of a simple, closed polygon is less than 180°, the polygon is called convex.

In contrast, an exterior angle (or external angle) is an angle formed by one side of a simple, closed polygon and a line extended from an adjacent side.

The sum of the internal angle and the external angle on the same vertex is 180°.

For example: x+35+75=180
x+110=180
x+110-110=180-110
x=70

The sum of all the internal angles of a simple, closed polygon can be determined by 180(n-2) where n is the number of sides. The formula can by proved using mathematical induction and starting with a triangle for which the angle sum is 180, and then adding a vertex and two sides, etc. A pentagon's internal angles add up to of 540 degrees (shown below)
180(n-2)= 180(5-2)= 180(3)= 540
Knowing this you can easily find the measure of each angle if it is a equiangular polygon with
\frac{180(n-2)}{n}.
So continuing from the above example with the pentagon:
\frac{540}{n}=\frac{540}{5}=108

(The exterior angle can be worked out by doing the following sum 360/number of sides in the equiangular polygon The interior angle can then be found by taking away the value of the exterior angle from 180. So in a pentagon there are 5 sides so to work out the exterior angle you do 360/5 =72 So the interior angle is 180-72=108 so the interior angle = 108 degrees)

The sum of the external angles of any simple closed (convex or concave) polygon is 360°.

The concept of 'interior angle' can be extended in a consistent way to crossed polygons such as star polygons by using the concept of 'directed angles'. In general, the interior angle sum in degrees of any closed polygon, including crossed (self-intersecting) ones, is then given by 180(n-2k) where n is the number of vertices and k = 0, 1, 2, 3. ... represents the number of total revolutions of 360o one undergoes walking around the perimeter of the polygon, and turning at each vertex, until facing in the same direction one started off from. In other words (or put differently), 360k represents the sum of all the exterior angles. For example, for ordinary convex and concave polygons k = 1, since the exterior angle sum = 360o and one undergoes only one full revolution walking around the perimeter.


External fertilization

thumb|[[Stony coral]] [[spawn (biology)|spawning]].External fertilization is a form of fertilization in which a sperm cell is united with an egg cell external to the bodies of the reproducing individuals. In contrast, internal fertilization takes place inside the female after insemination through copulation.

In sexual reproduction, there must be some way of getting the sperm to the egg. Since sperm are designed to be mobile in a watery environment (they have tails and are streamlined), aquatic animals can make use of the water in which they live. Many plants make use of external fertilization, especially ones without bright flowers or other means of attracting animals. In many aquatic animals such as coral or hydra, eggs and sperm are simultaneously shed into the water, and the sperm swim through the water to fertilize the egg in a process known as broadcast fertilization. In many fish species, including salmon, the female will deposit unfertilized eggs in the substrate and the male will swim by and fertilize them. External fertilization uses or needs thousands of sperm cells



From Yahoo Answers

Question:Describe one advantage of internal fertilization over exernal fertilization

Answers:You get to have FUN doing it

Question:What are the advantages and Disadvantages of each?

Answers:External- +requires less energy from the mother -it is easier for a preditor to get. Internal opposite of external

Question:I know everything about External and INternal Respiration i just would like to know in a simple chemistry formula and a short explanation why and how the O2 is used up and creates CO2. I know that O2 is needed for the body cells to work. This Question is aimed at medical students and doctors.

Answers:Oxygen does not create CO2. Oxygen is used as the final electron acceptor during electron transport. Without oxygen to accept electrons flowing down the ETS, the electrons stop flowing and ATP synthesis stops. CO2 is produced by the oxidative decarboxylation of pyruvate and two Kreb cycle intermediates.

Question:This is dealing with billing collections. I need at least 3 advantages & disadvantages for both internal & external collections. please help!!!!

Answers:Internal collections is more cost effective, it can be a simpler solution to leave out a third party for small business and it gives you complete access to your cases so that you are in the know of what's-what with which patient and his/her history. External collectors take the entire responsibility off your back and have the resources to take their cases to the end. While facilities alone usually can't afford to go after patients to the end, collection agencies are equipped with lawyers and ample methods. There's the additional advantage of convenience. Running after people's purses can be very difficult, especially if you're not used to being the 'bad guy'.

From Youtube

Internal Organs External - Products of Monkey Love :A completely improvised song from Episode 5 of the Products of Monkey Love podcast, subscribe and download the whole podcast for FREE from Itunes or last.fm This song has the beautiful piano tinkling of Mr James Uren, the solid awesome bassness of Mr Martin Uren, and the silly improvised singing of Mr Andy Jackson. The video was recorded at the Pizz studio in Brighton and was directed by Martin Uren. Please leave us comments and love, it's what keeps us going :) ... oh, and subscribe to our channel if you liked what you watched

Common Internal and External Tangents - YourTeacher.com :For a complete lesson on common internal and external tangents, go to www.yourteacher.com - 1000+ online math lessons featuring a personal math teacher inside every lesson! In this lesson, students learn the following theorems related to tangents. If a line is tangent to a circle, then the line is perpendicular to the radius at the point of tangency. If a line is perpendicular to a radius at its outer endpoint, then the line is tangent to the circle. If two tangent segments are drawn to a circle from an external point, then the tangent segments are congruent. Students are then asked to use these theorems to find missing segment lengths and missing angle measures in given figures. Students also learn the definitions of common internal tangents and common external tangents.