# Math Is Fun Forum

Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫  π  -¹ ² ³ °

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## #1 Help Me ! » help.... » 2007-05-28 03:12:13

0001T
Replies: 1

i am trying to solve this [t is time and T is temperature] to find the time t,

6450*Pi*(0.00185^2)*(0.0625)*836
dt = ---------------------------------------------   dT
(1.2^2)*7.5 - 108*Pi*0.00185*0.25*T

between the limits 0 and 180degC

can someone help me:D

## #2 Re: Help Me ! » vector cross product » 2007-03-28 15:53:24

this is a bit embarassing...because i had forgotten the basics:(

how do i solve this

-5db = 20log M(f)

## #3 Re: Help Me ! » vector cross product » 2007-03-28 15:15:37

I see.
Thank you so much.

## #4 Re: Help Me ! » vector cross product » 2007-03-28 13:59:52

Stanley_Marsh wrote:

I dont think you did wrong ,  cuz  4(3,0,4)=(12,0,16)

so if i present the surface normal as (12,0,16) it is not considered as wrong?

thanks

## #5 Help Me ! » vector cross product » 2007-03-28 13:19:59

0001T
Replies: 5

I am trying to solve this cross product; 3 vertices p1=(0,0,3), p2=(4,0,0) & p3=(0,4,3) given, I need to find the normal of the surface bounded by these 3 vertices.

I was told answer is (3,0,4) but my attempts kept leading me to (12,0,16)

here's what I did.

normal = (p1-p2) x (p3-p2) = [(0,0,3)-(4,0,0)]x[(4,0,0)-(0,4,3)] = (-4,0,3)X(4,-4,-3)

normal = (12,0,16)

where did i go wrong?

Thank you