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The term "radius" implies that we want to find the area of a pentagon inscribed in a circle. We have 5 triangles. Using trigonometry, each triangle has an area = (1/2)*(r^2)*sin(72º).

And since we have 5 triangles, the total area = (5/2)(r^2)*sin(72º)

Also, if we know the length of a side, the total area is given by 1.7204*(s^2) where s is the side length.

Re: how to covert km/h to m/s?

I believe this is something known as "dimensional analysis"

Here's the metod of conversion.....Suppose that some object is traveling at 100 Km/Hr, and we want to convert this to m/s......So we have

(100 Km/ 1 Hr) x (1Hr / 3600sec) X (1000m / 1 Km)

Note that we equated 1 Hr with 3600 sec and 1Km with 1000m

Also, notice that the  "Hr" and the "Km"  units "cancel out" and we're left with

(100) X (1/3600 sec) x (1000 m)  = 27.78 m/s

To convert m/s to K/hr, we just reverse the process

(27.78m/1sec) x (1Km/1000m) x (3600sec/1Hr)

Note now that the "sec" and "m" units cancel out and we're left with

(27.78) x (1Km/1000)x (3600/Hr) = 100Km/Hr

As long as we equate units properly, the final result should be in terms of what we're after. Also, some conversions may require us to equate more things to get the correct answer.  For instance, if we wanted to convert Km/year to cm/sec, it would require additional conversions.

I hope this helps.....

1 m/s = 1km/h * 1000 m/km * 1h/3600s

1km/h = 1 m/s * 1km/100m * 3600 s/h

42.4 grams = 424 decigrams

You treat each side as a triangle . The length of two of the sides are the radius. The angle between those two sides will be 72°. To calculate the length of the last side, you take half of the angle, so you get a triangle with a right angle. This allows you to use the sine function for the last side. But because you divided the angle by two, your result will be the third side's length divided by two.

Summarized:

Side 1 = Side 2 = r

Side 3 = 2*(sin(36°)*r)

I CHOOSE C

Hi all,

Great answers today from CPhill, SpawnofAngel, Alan, Bertie and Kitty<3.

The bugs are slowly being erradicated from the picnic that is web2.0calc forum.  Hopefully the members section and private messaging will be working soon.  I am also hoping that we will be able to post attachments in the not too distant future.

That is it for this Tuesday/Wednesday.

Melody 

The iteration in the previous post converges to the square root of 2.

For convergence to the square root of N, the formula should be

$$x_{i+1}=\frac{1}{2}\left(x_{i}+\frac{N}{x_{i}}\right)$$.

Coulomb's law says (1/4*pi*eps)*q*Q/r^2=F  where eps is the permittivity of free space (8.854*10^-12 farad/m) q is the charge on one source, Q is the charge on the other, r is the distance between them and F is the force.  This gives (1/4*pi*8.854*10^-12)(-6*10^-6)*Q/0.05^2=65

$${\mathtt{Q}} = {\frac{{\mathtt{65}}{\mathtt{\,\times\,}}{{\mathtt{0.05}}}^{{\mathtt{2}}}{\mathtt{\,\times\,}}{\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{\pi}}{\mathtt{\,\times\,}}{\mathtt{8.854}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{\left(-{\mathtt{12}}\right)}}{{\mathtt{\,-\,}}\left({\mathtt{6}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{-{\mathtt{6}}}\right)}} = {\mathtt{Q}} = -{\mathtt{0.000\: \!003\: \!013\: \!363\: \!313\: \!4}}$$Coulombs or about -3*10-6C

The potential energy is given by mass*g*height where g is the acceleration of gravity (9.81m/s^2), so energy used to heat silver is (1/3)*3.25*9.81*75 Joules

This energy equals mass*specific heat*temperature rise in the silver, so (1/3)*3.25*9.81*75 = 3.25*234*TempRise  which gives a temperature rise of

 $${\frac{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right){\mathtt{\,\times\,}}{\mathtt{9.81}}{\mathtt{\,\times\,}}{\mathtt{75}}}{{\mathtt{234}}}} = {\mathtt{1.048\: \!076\: \!923\: \!076\: \!923\: \!1}}$$ degrees C

I think that your question is finished. That's assuming I understand what you are asking.

e^1963 is the answer.

you need to find 2 numbers that multiply to -24 (from 3*-8) and add to -2

That would be -6 and +4

$$3y^2-2y-8\\\\
=3y^2-6y+4y-8\\\\
=3y(y-2)+4(y-2)\\\\
=(3y+4)(y-2)\\\\$$

$$\frac{4^6\times x^8 \times y^{-2}}{4^7}\times x^4y^2\\\\
=\frac{x^8 \times y^{-2}}{4}\times x^4y^2\\\\
=\frac{x^{12}}{4}$$

I have done it exactly as you have written it.

CPhill has done it as you quite likely intended. BUT if that is what you wanted then the stuff after the divide needed to be in brackets.

Why don't you use the site calculator? 

The first answer is good - as an approximation - but it is rounded to the nearest 100th not the nearest 10th

Exponential decay function is 

$$y=ab^x$$   where   $$a>0 \mbox{ AND } 0

The +1 at the end is insignificant.

It is the 3 that is wrong.  It needs to be a number between 0 and 1.

6 and a half - 3 and a quarter 

(6+1/2)-(3+1/4)

4 is the only square number that goes into 28 so

is you want to simplify sqrt(28) this is how

$$\sqrt{28}\\\\
=\sqrt{4\times 7}\\\\
=\sqrt{4}\times \sqrt{7}\\\\
=2\sqrt{7}$$

Mass–energy equivalence in Physics.

E is energy, m is mass, c is the speed of light.

E=mc^2

Albert Einstein

Mayhaps it is also doubled?

P1*V1*T1=P2*V2*T2

Maybe.

PV=nRT

Probably just use the divide sign and parenthesis to seperate things.

It would be a good idea for you to work through this.

http://www.mathsisfun.com/numbers/scientific-notation.html

5.29150262213

rounded to nerest tenth: 5.29

You haven't said how many inches = 1 foot  

Hi Kitty,

I see you have your username back.  Andre said he was going to email you a link. 

that question you just did you couold have cancelled the 3 with the 30, that may have been a smidge easier.  you probably thought of that and it certainly doesn't matter.

It is nice to see you on the forum.  It is always nice to see you.