Integrals in solve app?

[lrdheat]

Dumb question...can solve app accept integrals? (If so, how...)

[Helge Gabert]

Apparently so, e.g, in Home (Solve App),

type in the integral with the template

int(0,B,X^2 dX)=7 Solve -> 2.7589 ... for B.

Is this what you mean?

[lrdheat]

I'm getting bad guess messages...tried integral symbol, and also int(8*A-27*A^3,A,0,B)=3
Used guesses for B of .3 and solved for A in the solve app.

[lrdheat]

Rather, make that integral =.3

Bad guess error.

[lrdheat]

Also tried int(8*A-27*A^3,A,0,A)=.3 solving for A in the app with a guess of .3 and get bad guess message.

[Han]

In regular math type, you are asking the solver to solve:

\[ \int_0^B (8A-27A^3)\ dA = 0.3 \]

or equivalently

\[ 4B^2-\frac{27}{4}B^4 = 0.3 \]

… but you're asking the calculator to solve for A.

Quote:I'm getting bad guess messages...tried integral symbol, and also int(8*A-27*A^3,A,0,B)=3
Used guesses for B of .3 and solved for A in the solve app.

A is not even a variable in this equation. It appears in the integral, but it is a dummy variable, no? I do think there may be a bug of sorts since A is not truly a variable. So you should really only be allowed to solve for B. When A is set to its default value (of zero), you will generate an error because the calculator thinks you're integrating with respect to the "variable" 0 -- which of course makes no sense.

[Tim Wessman]

The problem is probably that you have the = sign inside the last argument for the integral. Make sure to push the right arrow to get all the way outside the integral template. What you are actually doing is most likely integral(...dA=.3) instead of integral(...dA)=.3

I try it and it works fine. returns ~.7103...

[DrD]

(10-22-2014 03:27 AM)Han Wrote:  In regular math type, you are asking the solver to solve:

\[ \int_0^B (8A-27A^3)\ dA = 0.3 \]

or equivalently

\[ 4B^2-\frac{27}{4}B^4 = 0.3 \]

Han,

You may already know this, but I've noticed that on some Android systems LaTex typeset gets mangled quite severely. It makes LaTex formatted math documents nearly illegible on some equipment. On others there is quite a delay for the LaTex format to resolve, with just the embedded Latex code viewable during the transition. {Samsung Galaxy S5, mangled it, Galaxy Note Pro takes awhile to resolve it.}

Sure looks great on Windows machines, making the math context much easier to realize. I thought it worthy of mention since some handheld devices may have trouble reading LaTex docs.

-Dale-

[lrdheat]

Thanks, Tim...

Integral sign from 0 to B for 8*A-27*A^3dA =Funtion.SignedArea/2 worked in the solve app (I had found the area under the curve for that function between root at zero, and root at about .54, and was curious to find at what point on the x domain beginning at zero would the signed area be half).

How do I write this in solve app using int()? I'm not having success with this entry method.

[Helge Gabert]

The integration variable should not show up in Solve Numeric View (this gives you the "Bad Guess(es)" message).

Try this: Enter the integral in Solve Symbolic View, but don't enter the equal sign - - stop right there (after the dX or whatever your variable of integration is) and press Enter (store in E1). Then, press the "Edit" touch key, enter the equal sign and the right hand expression, press Enter again. If you now go to the Solve Numeric View, is the integration variable still there? [You can also push the right arrow after the dX.]

It is possible that there is a "bug" in how the integral is stored in E1, . . . E9, E0. This can be seen in the plot window (soft key: Defn). If the "=" sign was entered in the first try in Solve Symbolic View (full equation), pressing the definition soft key shows that the integral is represented incorrectly.

[This is basically what Tim already described in the post above].

P.S. Regarding int() - - doesn't work in the solve app for me either - - use it in the CAS environment. fsolve in CAS is more powerful than the solve app anyway.

[Han]

(10-22-2014 05:27 PM)DrD Wrote:  You may already know this, but I've noticed that on some Android systems LaTex typeset gets mangled quite severely. It makes LaTex formatted math documents nearly illegible on some equipment. On others there is quite a delay for the LaTex format to resolve, with just the embedded Latex code viewable during the transition. {Samsung Galaxy S5, mangled it, Galaxy Note Pro takes awhile to resolve it.}

Actually, I was not aware of this. However, there is nothing that I personally can do about it. The math type is a feature of the forums, so that users may integrate mathematical expressions into their posts in a manner most commonly found in textbooks. You may want to PM Dave who runs the forums, or one of the moderators and bring this issue to their attention. With respect to the original post, the math type made it much more clear why A should not have been allowed as a variable.

[Didier Lachieze]

(10-22-2014 05:27 PM)DrD Wrote:  You may already know this, but I've noticed that on some Android systems LaTex typeset gets mangled quite severely. It makes LaTex formatted math documents nearly illegible on some equipment. On others there is quite a delay for the LaTex format to resolve, with just the embedded Latex code viewable during the transition. {Samsung Galaxy S5, mangled it, Galaxy Note Pro takes awhile to resolve it.}

For what it’s worth, the forum’s mathematical expressions are correctly displayed with just a small delay on both my old Android 2.2 phone and my Android 4.1 tablet.

[DrD]

I'm having much better results today (on the Galaxy S5), the Galaxy Note Pro tablet still takes quite awhile to convert LaTex codes to the intended math output. Maybe it has more to do with the browser app being used than the Android system. It may also have something to do with my wifi system. I don't know for sure. On the plus side, I get to see the actual Latex codes used to create the math formulas. That may be an unintended benefit!

I much prefer the LaTex typeset for legibility, so if it is just a problem on my side, then I can live with that just fine. I normally view the forum with Firefox on a Win7 system, and never see any similar issues.

-Dale-