Recent content by thornluke

I think my brain went dead, because I got it after saying that we assume the Sun as the volume of a sphere. So basically ly is the radius and we divide 75 by the volume of the star and galaxy to get the two answers :smile: Am I right?! Please approve! :approve:

The question assumes that the Sun is a sphere. So I suppose the volume element is sphere.

Homework Statement The number of stars around the Sun, within a distance of 17 ly, is 75. The number of galaxies in the local group, within a distance of 4.0 x106 ly from the Sun, is 26. Calculate the average popluation density, per ly3, of stars and galaxies. Homework EquationsThe Attempt...

C since v is the speed at rest, whilst V is the speed when the source is moving away. Is it possible to explain this by deriving different equations to λ + VT?

Homework Statement A source of sound emits waves of wavelength λ, period T and speed v when at rest. The source moves away from a stationary observer at speed V, relative to the observer. The wavelength of the sound waves, as measured by the observer is A. λ + vT B. λ - vT C. λ + VT D...

Is that a rule of some sort?

Not yet, I'm still new to this topic. In fact, I am still rather rusty with matrix multiplication, although I am getting better at it.

Homework Statement P=\begin{pmatrix}3 & -1\\ 2 & 4 \end{pmatrix} Q=\begin{pmatrix}4 & -1\\ -2 & 1 \end{pmatrix} R=\begin{pmatrix}3 & -3\\ 2 & 4 \end{pmatrix} S=\begin{pmatrix}4 & 7\\ 9 & 1 \end{pmatrix} PX = Q QY = R RZ = S Find Matrices X, Y, and Z. Homework...

Homework Statement When David goes fishing the probability of him catching a fish of type A is 0.45, catching a fish of type B is 0.75 and catching a fish of type C is 0.2. David catches four fish. If the event X is David catching two fish of type A and two other fish, the event Y is David...

Ah... 2 is a prime number too.. I see now. My mind has gone mad from all these probability questions..

Homework Statement Two tetrahedral dice (four-sided dice) are thrown. What is the probability that the sum of the scores is: a) even b) prime c) even or prime? Homework Equations The Attempt at a Solution a) P(even) = 1/2 b) P(prime) = 9/16 c) c for confused :confused: Can...

Thanks very much. Can't believe I can't even think simple.

Ahh.. I think I'm starting get the grasp of this.. one more problem! Expand (2+x)5 and hence find 1.95 = 32 + 80x+ 80x2 + 40x3 + 10x4 + x5 Why can 1.95 be considered to be x= -0.1 in the above expansion?

I am so lost here.. why am I so terrible at maths :frown:

So...the expansion of [2x+(1/x)]5 must have a constant term or a term in x-1... Constant term means the term with no x right? But why can the term independent of x be in x-1 too?