Math Is Fun Forum

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

You are not logged in.

#9951 Re: Puzzles and Games » Euclidean Geometry » 2010-07-03 00:35:13

Bob

whoops.  I've got BBCode on but my image tag hasn't worked.

What no FAQs on how to post images?

But you can follow the link to my site for the diagram

EDIT No you cannot.  See post 24.

#9952 Puzzles and Games » Euclidean Geometry » 2010-07-03 00:33:03

Bob
Replies: 26

diagram in post 24.

The diagram shows a triangle ABC

with ABC = 80 and ACB = 80

D lies on AC so that DBC = 60

and E lies on AB so that ECB = 50.

To find (by Euclidean geometry) x = EDB

#9953 Re: Help Me ! » Use the compound interest formula » 2010-07-01 04:26:52

Bob

"annual rate = 10%  monthly rate = 10%/12"

Don't think so.

monthly multiplier = (1.10)^(1/12)  = m (say)  [ so that 12 monthly multpliers give the yearly multiplier]

then monthly rate = (m-1) x 100 %  [ to convert back to percentage ]

#9954 Re: Introductions » Square problem: » 2010-07-01 03:46:35

Bob

ABCD has area    3    x    3     =    9     =    9 ^   1
EFCG has area     1    x    1     =    1     =    9 ^   0
HICJ has area    1/3   x   1/3   =   1/9   =    9 ^   -1
KLCM has area   1/9   x   1/9   =  1/81  =    9 ^   -2
.....                           ....                   .....               
10th square has area 3^ -8  x   3 ^ -8  =    9 ^   -8

#9955 Re: Help Me ! » Use the compound interest formula » 2010-07-01 03:33:38

Bob

I don't think this is a straight compound interest.  You can use CI when a fixed sum is invested but Dharshi says there's an annual investment.  So new money has to be added each year in addition to the interest.

Before I work out a revised formula let's just check I've got it right:

(i)  each year $1 is invested 

(ii)  for 20 years

(iii) interest rate is compound (ie. add the calculated interest  to the investment for the next year)

(iv) 10% per month !  This seems a bit generous!  Did you mean an equivalent annual rate of 10% but calculated monthly?

#9956 Re: Help Me ! » Geodesic Dome Dihedral » 2010-06-26 21:06:31

Bob

There are lots of these.  Try

http://mathworld.wolfram.com/GeodesicDome.html

Hope this helps

#9957 Re: Help Me ! » entering a function into graphing calculator » 2010-06-20 01:15:20

Bob

The graph of Y^2=X should be a symmetrical parabola (like Y = X^2 but 'on its side'). 

If you use sqrt you'll only get half the graph because the calc will default to the positive root.  To get the whole graph plot two functions:

Y1=sqrt(x) and Y2=negative sqrt(x) [note : use the negative key not the subtract key]

Board footer

Powered by FluxBB