Q1 of 95 Page 72

Now compute the squares of these numbers in head:
52

Using (x+y)² = x² + xy +yx +y²

(52)² = (50 + 2)²

=(50)² + 2×50×2 + (2)

= 2500 + 200 + 4

= 2704

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

Multiply the diagonal pairs and find the difference of these products.

3 × 19 = 57

17 × 5 = 85

85 – 57 = 28

Explain using algebra, why the difference is always 28 (It is convenient to take the number at the centre as x).

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

Multiply the diagonal pairs and find the difference of these products.

3 × 19 = 57

17 × 5 = 85

85 – 57 = 28

Explain using algebra, why the difference is always 28 (It is convenient to take the number at the centre as x).

Now compute the squares of these numbers in head:

105

Questions · 95

4. Identities

1 1 1 1 1 1 2 2 2 2 2 2 3 3 4 4 1 1 1 2 2 2 2 2 2 3 3 4 4 5 5 1 1 1 1 1 1 1 1 2 2 3 3 3 3 1 1 1 1 1 1 1 1 1 1 1 1 2 2 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 1 1 1 1 2 2 2 2 3 3 3 3 1 1 1 1 1 1 1 1

Now compute the squares of these numbers in head:52