Member: Rom

7 Questions
2456 Answers

1225

+6251

is there any point to answering these anymore?

Does anyone even look at the answers given?

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Rom Mar 3, 2020

1762

+6251

latex delimiters

Is there a way of embedding LaTex into posts w/o using the LaTex button and dialogue?

Other boards have $$, [tex][/tex], [math][/math]
read more ..

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Rom Aug 8, 2019

1806

+6251

You know what guarantees I won't look at your problem?

Using the words ASAP, or fast, or now, or anything similar in your title.

You're all quite fortunate to have the group of us here that answer your questions.
read more ..

off-topic

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Rom Jan 4, 2019

1303

+6251

sub forums

It might be nice to have a few sub forums so we know better how to address given problems.

For example I suspect we sometimes use calculus to answer questions posted by people in pre-calculus classes.
read more ..

Rom Nov 27, 2018

1466

+6251

Why do sometimes we get the option to filter out answered questions but sometimes we don't?

off-topic

GingerAle ●●●●●●●●

Rom Nov 15, 2018

+26

3062

+6251

I'm concerned that we are just doing people's homework for them. That's no way to encourage people to actually learn the math.

I'm concerned that we are just doing people's homework for them. That's no way to encourage people to actually learn the math.

Thoughts?

CPhill ●●●●●●●●●●●●●●●●●●

Rom Oct 16, 2015

1700

+6251

help file?

Is there a help file somewhere on how to use the forum tools to get a decent math output display?
Does this board support LaTex?

Melody ●

Rom Jan 30, 2014

+6251

Quote:
log28=log4+logx

get the constants on one side and x on the other

logx = log28 - log4

then use a law of logs to combine log28 - log4 into a single term. Do you remember how to do that?

logA - logB = log(A/B)

see if you can finish it

RomFeb 3, 2014

+6251

Quote:
why does everyone love math i only like meserment

Who is this everyone you speak of? Most folks I know either don't like or don't care about math.

If you like measurement you might learn to spell it properly!

RomFeb 3, 2014

+6251

a mole? like this? http://24.media.tumblr.com/tumblr_m8jlf21t7V1qghjizo1_250.jpg ?

Assuming you mean a million you just divide 1,000,000 by 100

1000000/100 = 10000

this would be 100 of those bundles you see in briefcases in spy flicks.

RomFeb 3, 2014

+6251

Quote:
-7* (natural logarithm) ln(2x)=4

-7 ln(2x) = 4

ln(2x) = -4/7

e ^ln(2x) = e ^-4/7

2x = e ^-4/7

x = 1/2 e ^-4/7

RomFeb 3, 2014

+6251

Compound interest just takes a given annual rate, divides it by some number of periods per year K, and applies that new interest rate K times a year.

The formula for the future value, given rate r, over N years, compounded K times a year is

FV = PV*(1+r/K) ^KN

To compare, let's say you have 5% annual interest

Compounded annually you would have, over say 30 years

FV = PV*(1+0.05) ³⁰

FV/PV = 4.322

Compounded quarterly you would have

FV = PV*(1+0.05/4) ^4*30 = PV*(1+0.0125) ¹²⁰

FV/PV = 4.440

For equal rates and years and present values compounding yields a higher future value.

Now how does this relate to exponential growth?

If you recall exponential growth is described by

f(t) = f0*e ^g*t where f0 is the initial value of f and g describes the growth or decay rate. Positive g is growth, negative g is decay. A higher value of g leads to faster growth or decay.

now rewrite your compound interest formula as a function of t years

FV(t) = PV*(1+r/K) ^K*t

remembering that b ⁿ = e ^n*log(b) we get

FV(t) = PV*e ^{log(1+r/K)*K*t}

i.e. FV(t) is exponential growth with

f0 = PV
g = log(1+r/K)*K

RomFeb 3, 2014

+6251

262144 = 2 ¹⁸

RomFeb 3, 2014

+6251

Quote:
how to use degress minutes and seconds with sin

there are 2 cases

a) your sin function can accept an input angle in degrees
b) your sin function must take an input angle in radians

a) All you have to do here is convert minutes and seconds to a decimal fraction of a degree. The formula is

Total_Degrees = Degrees + Minutes/60 + Seconds/3600

and you would use sin(Total_Degrees)

b) In this case you have to further convert Total_Degrees to radians and as there are 2*Pi radians in a 360 degree circle we have

Total_Radians = Total_Degrees * (Pi/180) radians

and you would use sin(Total_Radians)

RomFeb 3, 2014

+6251

Quote:
If I put $150 in an account that earns 7%, how much will there be in the account at the end of 30 years?

You need to specify that the interest is compounded annually (as opposed to quarterly or monthly) but assuming that we have

FV = future value
PV = present value
r = rate
t = time in years

FV = PV(1+rate) ^t

and in this case we have

FV = $150(1+0.07) ³⁰ = $1141.84

RomFeb 3, 2014

+6251

Quote:
calculate the current flowing through the circuit of a toy car that has a resistance of 20 and is powered by a 3 volt battery

Ohm's law states that

Current = Voltage/Resistance

so in this case we have

Current = 3 volts/(20 ohms) = 0.15 amps = 150 milliamps

RomFeb 3, 2014

+6251

to do them? what do you mean?

to get the integers take all the positive numbers 1, 2, 3 .....
now take the negative of each one of those -1, -2, -3....
now add 0.
All of those numbers together make up the integers.

take any two integers a and b, where b isn't 0. a/b is then a rational number

To get the irrational numbers take all of the real numbers.
Now toss out the rational numbers. What's left is the irrational numbers.

RomFeb 2, 2014

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