Wikipedia:Reference desk/Archives/Mathematics/2012 December 14

= December 14 =

The Laplacian
For the Laplacian operator, should one use Δ (U+0394: GREEK CAPITAL LETTER DELTA) or ∆ (U+2206: INCREMENT)? --Andreas Rejbrand (talk) 11:27, 14 December 2012 (UTC)


 * The Unicode standard lists under U+2206: INCREMENT = Laplace operator, but makes no such reference under U+0394. From this I would take it that U+2206 is the appropriate character to use. — Quondum 12:20, 14 December 2012 (UTC)


 * Thank you for your reply. I had made the same observation, so I'd guess this is correct. --Andreas Rejbrand (talk) 20:10, 14 December 2012 (UTC)

sequence which is not in any l^p
Find a sequence which converges to 0 but not in any l^p ,where p>=1.Is this sequence 1/ln(n+1) or 1/(n^1/p)plz help me to understand it.. — Preceding unsigned comment added by 182.187.28.118 (talk) 12:00, 14 December 2012 (UTC)
 * It's the former. "Not in any l^p" means you first choose the sequence and then for any p you choose it will not be in l^p. You can't refer to p itself when choosing the function. -- Meni Rosenfeld (talk) 12:56, 14 December 2012 (UTC)

Am I right?
3cos4x * 4 = 12cos4x? --84.110.173.27 (talk) 17:51, 14 December 2012 (UTC)


 * Ambiguous as written. It depends on where you put the parens:


 * 3(cos4x) * 4 = 12(cos4x)


 * 3cos(4x) * 4 = 12cos(4x)


 * 3cos(4x * 4) ≠ 12cos(4x)


 * StuRat (talk) 17:54, 14 December 2012 (UTC)

thanks, 1. what the difference between: 12cos(4x) to 12(cos4x)?

2. y' (3sin4x) = 4*3sinx = 12cos4x right? --84.110.173.27 (talk) 09:38, 15 December 2012 (UTC)


 * 1: No difference. They both mean 12 ⋅ (cos(4x)), and may also be written 12 cos 4x.
 * 2: Reading between the lines, you mean: "y = 3 sin 4x, so y′ = 4 ⋅ 3 cos 4x = 12 cos 4x, right?", to which the answer is "Yes, if by the prime you mean the derivative with respect to x". — Quondum 10:21, 15 December 2012 (UTC)