The important thing to grasp is the relationship between 1 and 4.
If you imagine a pyramid made of square blocks, which five blocks (units) high and has five blocks along its base (25 blocks). It isn't important that it be pointed at the top.

Diag 3

 

Diag 5 Centre of a Helium nucleus.





 

 A sphere can also be defined as the surface formed by rotating a circle about any diameter. If the circle is replaced by an ellipse, and rotated about the major axis, the shape becomes a prolate spheroid, rotated about the minor axis, an oblate spheroid.

 Circumference of a circle

The circumference of a circle is the length around it. The circumference of a circle can be calculated from its diameter using the formula:

c=\pi\cdot{d}.\,\!

Or, substituting the radius for the diameter:

c=2\pi\cdot{r}=\pi\cdot{2r},\,\!

where r is the radius and d is the diameter of the circle, and the Greek letter π is defined as the ratio of the circumference of the circle to its diameter. The numerical value of π is 3.141 592 653

 
 

 

 

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