# Life long sharing . . .

## Archive for July 2016

### Maths Olympiad – Practice 21

Posted on: July 21, 2016

### Maths – something important

Posted on: July 21, 2016

I personally think these are something fundamental one must master before they move on to Algebra.

### Maths Olympiad – Another interesting Venn Diagram problem

Posted on: July 20, 2016

### Science – The 24 Solar Terms

Posted on: July 20, 2016

Solar Terms is a calendar of twenty-four periods and climate to govern agricultural arrangements in ancient China and functions even now.

Here is the English version I found from the web:

### Scienec – Solstices, Equinox, Aphelion, Perihelion

Posted on: July 20, 2016

Still confused about Solstices, Equinox, Aphelion, Perihelion?

Hope this picture helps:

Look at the picture, as you can see,
1.  the Sun is not in the middle of the Earth’s orbit.
2. the seasons 四季 on Earth is not caused by the distance from Sun, it’s caused by the “TILT” 倾斜 of Earth’s axis.
3. When the Earth is at “aphelion” (furthest to the Sun) it’s Summer in Northern hemisphere 北半球
4. When the Earth is at “perihelion” (closest to the Sun) it’s Winter in Northern hemisphere

### Maths Olympiad – More Venn Diagram questions

Posted on: July 19, 2016

In questions involve 3 groups (3 circles in the diagram), it sometimes takes time to understand why

Total = A+B+C – A∩B – B∩C – A∩C + A∩B∩C

Putting up this slides in hope it helps in visualize how we reach the above.

### Science – Space Science – Why the same side of the moon always faces the Earth

Posted on: July 18, 2016

This video is a bit too quiet, but very informative.

### Science – Space Science – Albedo

Posted on: July 18, 2016

We come across this term “albedo” and I find the picture explains it very well:

Here is the definition:

### Maths – Centroid theorem

Posted on: July 15, 2016

This is a brief and clear video explaining Centroid theorem and how to use it.

### Maths – Alcuin’s Sequence

Posted on: July 14, 2016

“How many triangles with integral side lengths are possible, provided their perimeter is 3636 units?”

To solve the above problem, we can use the Alcuin’s sequence:

Now, let’s try another question:

How many possible triangles are there with perimeter of 12 and sides of integral length?

** integral length – the length is integer