Take nine numbers forming a square in a calendar and mark the four numbers at the corners.

Add the squares of diagonal pairs and find the difference of the sums.

3² + 19² = 370

17² + 5² = 314

370 – 314 = 56

Do this for other such nine numbers.

Mark four numbers forming a square in a calendar:

Add the squares of the diagonal pair and find the difference of these sums:

4² + 12² = 160

11² + 5² = 146

160 – 146 = 14

Explain using algebra, why the difference is 14 always.

Take nine numbers forming a square in a calendar and mark the four numbers at the corners.

Add the squares of diagonal pairs and find the difference of the sums.

3² + 19² = 370

17² + 5² = 314

370 – 314 = 56

Do this for other such nine numbers.

Take nine numbers forming a square in a calendar and mark the four numbers at the corners.

Add the squares of diagonal pairs and find the difference of the sums.

3² + 19² = 370

17² + 5² = 314

370 – 314 = 56

Explain using algebra, why the difference is always 56. (it is convenient to take the number at the centre of the squares as x – see the section, Another trick of the lesson, Unchanging Relation of the Class 7 textbook)

Take nine numbers forming a square in a calendar and mark the four numbers at the corners.

Add the squares of diagonal pairs and find the difference of the sums.

3² + 19² = 370

17² + 5² = 314

370 – 314 = 56

Explain using algebra, why the difference is always 56. (it is convenient to take the number at the centre of the squares as x – see the section, Another trick of the lesson, Unchanging Relation of the Class 7 textbook)