Viewing Thread:
"Maths Question"

I'm doing maths homework sheet and nearly finished it...

It is on vectors and the first question is easy but I don't know what to do for some reason...

Calculate length of vector a:

a = 5i + 2/2j - 4/3k

/ = square root

So what do I do?

SHEEPY wrote:
> I'm doing maths homework sheet and nearly finished it...

It is on vectors and
> the first question is easy but I don't know what to do for some
> reason...

Calculate length of vector a:

a = 5i + 2/2j - 4/3k

/ = square
> root

So what do I do?]


go to sleep...

How good am I! Anyone wanna touch me???

TOUCH ME!

Sonic

exact
> value of sin 2A if sin A = 3/4

0

hmmm... this is my worst area of matsh... but hey!

sin2A= 2 * sinA * cosA
sin2A= 2 * (3/4) * cosA

Now, cos sq + sin sq = 1
so cosA = ROOT(1-sin(sq))
cosA = root(7/16)

Since A is between 0 and 2pi, then cosA is positive, so we take the POSITIVE root only!

therefore
sin2A = 2 * (3/4) * (root7)/4
= [6 * ROOT(7)]/16
=3ROOT(7) / 8

Sonic

You all need help. Maths on a Sunday?

a = 5i + 2/2j - 4/3k

I think someone got it... but basically it's just pythagoras- take the root of the sum of the squares of each side.

So, 5 sq + 2/2 sq + 4/3 sq = 25 + 8 + 48 = 81

And the length is just the root of this answer = 9

Sonic

Actually I did do the same way as Venom...

I always get the fecking hard ones and forget how to do the simple stuff.

Yay I got it right without your help :)

Venom was correct though, answer was 9:

I did it this way

square root of:

i squared
j squared
k squared

and it came out 9... hard to replicate it on keyboard :)

----

Thats me done 12 sides of paper and only 1 more left:

exact value of sin 2A if sin A = 3/4

0
Hmmm

Think I change 3/4 to 3pie/4 then use formula, bah.

1 + 1 = 3

If thats what you mean.

This is why I dropped Maths in school...

I take it i, j & k are the unit vectors on the x, y& z axes.
They should be. Then its just Pythagorus in three dimensions:

For eg

a = xi + yj + zk

gives length of a to be:

/(x^2 + y^2 + z^2)

/ is sqrt again and x^2 means x squared. Just stick in the values for x, y and z (5, 2/2 and 4/3 in this case)
I wont give you the answer, but it should be a whole number I think.

Any other qu's, I'm always happy to help.