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Wilmer
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Today,
00:02
MarkFL
replied to a thread
2.2.8 de xy'+2y=sin x,y(pi)=1/pi find solution
in
Differential Equations
You wound up with $x^2\sin(x)$ on the RHS before integrating, but it should be $x\sin(x)$. :)
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2 replies | 54 view(s)
Yesterday,
19:23
MarkFL
replied to a thread [SOLVED]
2.2.7 de with trig and y(1)=1
in
Differential Equations
When you multiply through by $\mu(x)$, you should have: \frac{d}{dx}(\sin(x)y)=2 And then integrate: \sin(x)y=2x+c_1 ...
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2 replies | 36 view(s)
June 19th, 2018,
19:21
MarkFL
replied to a thread
2.2.6 de with e^x
in
Differential Equations
Towards the end, when you divide through by $x$, you want: y(x)=\frac{e^x}{x}+\frac{c}{x} You mistakenly divided the constant by $e^x$.
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1 replies | 41 view(s)
June 19th, 2018,
15:31
MarkFL
replied to a thread
2.2.5 de equation with y(1)=1/2
in
Differential Equations
Yes, but you used it on the original ODE, not the one in standard linear form. :)
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4 replies | 91 view(s)
June 18th, 2018,
07:29
Wilmer
replied to a thread
Present Value Maths
in
Other Topics
Book is correct. Are you using a calculator? You're probably entering the data wrongly...we can't tell... Try it this way: u = (1.02/1.10)^10 v =...
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2 replies | 65 view(s)
June 17th, 2018,
12:39
MarkFL
replied to a thread [SOLVED]
2.2.3 de with tan x
in
Differential Equations
I can't imagine trying to use the internet on a telephone. I'm sorry scrolling on a telephone is such a chore...they should fix that.
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8 replies | 113 view(s)
June 17th, 2018,
00:59
MarkFL
replied to a thread [SOLVED]
2.2.3 de with tan x
in
Differential Equations
Are you using Tapatalk by any chance? I have code in place to let me know when posts have been edited, so I don't miss added content (it's better to...
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8 replies | 113 view(s)
June 17th, 2018,
00:52
MarkFL
replied to a thread [SOLVED]
2.2.3 de with tan x
in
Differential Equations
When you multiply by $\mu(x)$, you get: \sec(x)y'+\tan(x)\sex(x)y=\sec(x)\sin(2x) This can be written as: ...
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8 replies | 113 view(s)
June 16th, 2018,
19:51
MarkFL
replied to a thread [SOLVED]
2.2.3 de with tan x
in
Differential Equations
-\ln(\cos(x))=\ln\left((\cos(x))^{-1}\right)=\ln(\sec(x))
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8 replies | 113 view(s)
June 16th, 2018,
19:38
MarkFL
replied to a thread [SOLVED]
2.2.3 de with tan x
in
Differential Equations
\mu(x)=\exp\left(\int \tan(x)\,dx\right)=e^{\Large\ln(\sec(x))}=\sec(x)
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8 replies | 113 view(s)
June 16th, 2018,
09:40
Wilmer
replied to a thread
Problems with Percentage
in
Pre-Algebra and Algebra
https://percentagecalculator.net/ "percent" means "per hundred" Simple example: 200 increases to 218: that's "9 per hundred", right?...
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6 replies | 126 view(s)
June 16th, 2018,
00:29
MarkFL
replied to a thread
Problems with Percentage
in
Pre-Algebra and Algebra
300+300\cdot\frac{1666}{100}=300(1+16.66)=300\cdot17.66=5298 Here, we have taken 300, and added 1666% of 300 to it. However if we multiply 300 by...
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6 replies | 126 view(s)
June 15th, 2018,
16:28
MarkFL
replied to a thread [SOLVED]
2.2.1 de with u substitution
in
Differential Equations
\mu(x)=\exp\left(\int\frac{1}{x}\,dx\right)=e^{\ln(x)}=x
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3 replies | 63 view(s)
June 15th, 2018,
15:53
MarkFL
replied to a thread [SOLVED]
2.2.1 de with u substitution
in
Differential Equations
We can see the integrating factor is $\mu(x)=x$ and so the ODE will become: \frac{d}{dx}(xy)=x\sin(x) Upon integrating, we get: ...
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3 replies | 63 view(s)
June 15th, 2018,
14:14
MarkFL
replied to a thread
2.1.9 de with reciprocal
in
Differential Equations
That's fine giving $x$ as a function of $y$...I just chose to give $y$ as a function of $x$ since the original equation has $x$ as the independent...
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4 replies | 73 view(s)
June 15th, 2018,
12:44
MarkFL
replied to a thread
2.1.9 de with reciprocal
in
Differential Equations
We could also simply state: \d{x}{y}=e^y-x \d{x}{y}+x=e^y Now, our integrating factor is: \mu(y)=\exp\left(\int\,dy\right)=e^y
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4 replies | 73 view(s)
June 15th, 2018,
03:08
MarkFL
replied to a thread
2.1.9 de with reciprocal
in
Differential Equations
I would begin here with the substitution: u=e^y\implies u'=uy' And so the ODE becomes: \frac{1}{u}u'=\frac{1}{u-x} Or:
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4 replies | 73 view(s)
June 14th, 2018,
19:11
Wilmer
replied to a thread
Tricky equation
in
Pre-Algebra and Algebra
Gotcha! Thanks again...
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4 replies | 97 view(s)
June 14th, 2018,
16:27
Wilmer
replied to a thread
Tricky equation
in
Pre-Algebra and Algebra
I was able to get to: w = SQRT As you probably surmised, this is Heron's triangle area in disguise! Example: triangle sides u,v,w: u=4, v=13,...
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4 replies | 97 view(s)
June 14th, 2018,
13:56
Wilmer
started a thread
Tricky equation
in
Pre-Algebra and Algebra
a^2 = k(k-u)(k-v)(k-w) where 2k = u+v+w Given a, u and v, w = ?
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4 replies | 97 view(s)
June 14th, 2018,
11:23
MarkFL
replied to a thread
Rationalize expression
in
Pre-Algebra and Algebra
Hello and welcome to MHB! (Wave) I've moved this thread to our elementary algebra forum, since this is a better fit for the problem and I've give...
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2 replies | 89 view(s)
June 11th, 2018,
21:08
MarkFL
replied to a thread
2.1.{8} de with trig y(pi)=0
in
Differential Equations
You now have the correct integrating factor, but you didn't multiply the RHS by this factor. :) You should eventually get: ...
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4 replies | 78 view(s)
June 11th, 2018,
19:17
MarkFL
replied to a thread
2.1.{8} de with trig y(pi)=0
in
Differential Equations
Your integrating factor is incorrect. Try finding that again. :)
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4 replies | 78 view(s)
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June 14th, 2018
19:11 -
Wilmer
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Re: Tricky equation
by
mrtwhs
I was able to get to: w...
18:28 -
Wilmer
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Re: Tricky equation
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mrtwhs
a^2 = k(k-u)(k-v)(k-w)...
June 8th, 2018
18:47 -
Wilmer
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Re: How to use the RATE function in Excel ?
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tkhunny
Not familiar with Excel;...
18:41 -
tkhunny
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Re: How to use the RATE function in Excel ?
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Wilmer
Not familiar with Excel;...
June 7th, 2018
13:13 -
caffeinemachine
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Re: Jokes
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Wilmer
Pretty good, Mr.Fly! ...
09:00 -
Wilmer
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Roman numerals remind me...
June 6th, 2018
14:40 -
I like Serena
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Wilmer
Before I forget it: you...
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Wilmer
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Once my student raised...