If 1² + 2² + 3² ...... + x² = = x(x

If 1² + 2² + 3² ...... + x² = = x(x + 1) (2x + 1) then 1² + 3² + 5² + ..... 19² is equal to
2

From the question ,

1² + 2² + 3² + ..... + n² =	n(n + 1)(2n + 1)
	6

∴ 1² + 3² + 5² + ..... + 19² = (1² + 2² + 3² + ..... + 20²) – (2² + 4² + ..... + 20²)

∴ 1² + 3² + 5² + ..... + 19² =	20(20 + 1)(40 + 1)	– 2² (1² + 2² + ..... + 10²)
	6

Required answer =	20 × 21 × 41	-	4 × 10 (10 + 1)(20 + 1)
	6		6

Required answer = 2870 – 1540 = 1330

If 1² + 2² + 3² ...... + x² = =	x(x + 1) (2x + 1)	then 1² + 3² + 5² + ..... 19² is equal to
	2