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# If 3=4x+1 what is x

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If 3=4x+1 what is x

If 10=12-3x what is x

If 3-x = 10 what is x

kathrynplum  May 3, 2014

#12
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Ok, just figured how to enter matrices.  You need square brackets, so:

[[1, 2],[3, 4]]*[[5, 6],[7, 8]] gives:

$$\begin{bmatrix} {{\mathtt{1}}} & {{\mathtt{2}}}\\ {{\mathtt{3}}} & {{\mathtt{4}}}\\ \end{bmatrix} {\mathtt{\,\times\,}}\begin{bmatrix} {{\mathtt{5}}} & {{\mathtt{6}}}\\ {{\mathtt{7}}} & {{\mathtt{8}}}\\ \end{bmatrix} = \begin{bmatrix} {{\mathtt{19}}} & {{\mathtt{22}}}\\ {{\mathtt{43}}} & {{\mathtt{50}}}\\ \end{bmatrix}$$

Alan  May 4, 2014
Sort:

#1
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you can use the built in "equation solver" to verify your solutions:

#2
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I'm experimenting

$$\underset{\,\,\,\,{{\rightarrow {\mathtt{x}}}}}{{solve}}{\left({\mathtt{3}}={\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{x}}{\mathtt{\,\small\textbf+\,}}{\mathtt{1}}\right)} = \underset{{\tiny{\text{Error: Unknown Function 'solve'}}}}{\underset{\,\,\,\,{{\rightarrow {\mathtt{x}}}}}{{solve}}{\left({\mathtt{3}}={\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{x}}{\mathtt{\,\small\textbf+\,}}{\mathtt{1}}\right)}}$$

No it doesn't work straight from the forum!

You have to do it from the calculator itself.

What a pity!

Thanks for showing us that admin I like the new fraction calc too!!

Melody  May 4, 2014
#3
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Here, you just need to put:

$${\mathtt{3}} = {\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{x}}{\mathtt{\,\small\textbf+\,}}{\mathtt{1}} = {\mathtt{x}} = {\frac{{\mathtt{1}}}{{\mathtt{2}}}}$$

using the Math(Input=Result) tab.

Alan  May 4, 2014
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Thanks Alan

Melody  May 4, 2014
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Alan, can you get the other calcs working from the forum, like the matrix or the fraction calc?

Melody  May 4, 2014
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In Math(Input=Result) put (1, 2, 3)+(4, 5, 6) to get

$$\begin{pmatrix} {\mathtt{1}} \\ {\mathtt{2}} \\ {\mathtt{3}} \end{pmatrix} {\mathtt{\,\small\textbf+\,}}\begin{pmatrix} {\mathtt{4}} \\ {\mathtt{5}} \\ {\mathtt{6}} \end{pmatrix} = \begin{pmatrix} {\mathtt{5}} \\ {\mathtt{7}} \\ {\mathtt{9}} \end{pmatrix}$$

(1, 2, 3)*(4, 5, 6) gives (though it seems to appear in white (so difficult to see) in the Math box!

$$\begin{pmatrix} {\mathtt{1}} \\ {\mathtt{2}} \\ {\mathtt{3}} \end{pmatrix} {\mathtt{\,\times\,}}\begin{pmatrix} {\mathtt{4}} \\ {\mathtt{5}} \\ {\mathtt{6}} \end{pmatrix} = {\mathtt{32}}$$

Odd! It goes white here after I type Publish (but was visible to me before that)!  Still some bugs in the system!

Now it's visible again!!!!

Haven't figure out how to enter matrices yet -  will experiment!

Alan  May 4, 2014
#7
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Thanks Alan,

Shouldn't the second one be a 1 by 3 matrix for this to work.

If I had seen this working when i was teaching i would have marked it as wrong!

Melody  May 4, 2014
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(1, 2)^T*(3, 4)

$${\begin{pmatrix} {\mathtt{1}} \\ {\mathtt{2}} \end{pmatrix} }^{{\mathtt{T}}}{\mathtt{\,\times\,}}\begin{pmatrix} {\mathtt{3}} \\ {\mathtt{4}} \end{pmatrix} = \begin{pmatrix} {\mathtt{11}} \end{pmatrix}$$

Fractions (use a colon):

1:2

$${\frac{{\mathtt{1}}}{{\mathtt{2}}}} = {\mathtt{0.5}}$$

Using Math(Input) (not Math(Input= Result) we have

2*(x:3)

$${\mathtt{2}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{x}}}{{\mathtt{3}}}}\right)$$

Using Math(Input = Result) we have

2*(x:3)=6

$${\mathtt{2}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{x}}}{{\mathtt{3}}}}\right) = {\mathtt{6}} = {\mathtt{x}} = {\mathtt{9}}$$

Alan  May 4, 2014
#9
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Melody said:

Shouldn't the second one be a 1 by 3 matrix for this to work. (referring to 3x1 vector multiplied by another 3x1 vector).

If I had seen this working when i was teaching i would have marked it as wrong!

Yes, I too don't like this! You can put in a transpose (see my other post), which is preferable, but the system used here also seems to be happy with doing it this way.  It isn't unique in this respect.  Mathcad allows the same (what is to my mind) sloppiness (Matlab doesn't)!

Alan  May 4, 2014
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Alan,

do you get how the numbering system works for the posts in here.

Each post has its own number but there is a number for the question thread too.

Have you worked out how they tie together?

Melody  May 4, 2014
#11
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I don't see numbers against individual posts, only page numbers.  I haven't observed anything special about them.  Am I missing something?

Alan  May 4, 2014
#12
+26399
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Ok, just figured how to enter matrices.  You need square brackets, so:

[[1, 2],[3, 4]]*[[5, 6],[7, 8]] gives:

$$\begin{bmatrix} {{\mathtt{1}}} & {{\mathtt{2}}}\\ {{\mathtt{3}}} & {{\mathtt{4}}}\\ \end{bmatrix} {\mathtt{\,\times\,}}\begin{bmatrix} {{\mathtt{5}}} & {{\mathtt{6}}}\\ {{\mathtt{7}}} & {{\mathtt{8}}}\\ \end{bmatrix} = \begin{bmatrix} {{\mathtt{19}}} & {{\mathtt{22}}}\\ {{\mathtt{43}}} & {{\mathtt{50}}}\\ \end{bmatrix}$$

Alan  May 4, 2014
#13
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Thanks Alan for the matrix info.

With regards to the page numbering, yes, I think you are missing something.

It is very obscure.  sometimes individual post in a thread can be referenced but I don't understand it.  I have deleted the duplicates now but in my temporary sticky questions today I referenced threads and they doubled up even though the numbers were different.  I have known this is the case for some time but as I said, I do not understand how it works or how i can make proper use of it.

Oh, on the answer page, individual posts, not threads, are referenced all the time.

Also if you do a search - which isn't working very well yet - often a post will come up but it is stand alone, the thread it belongs to is nowhere in sight!

Melody  May 4, 2014

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