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### Feedback

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### History

#### Checkpoint description

Describe what's changed since the last checkpoint.

#### Chris Graham1 year, 11 months ago

The pattern match on line 10 of the custom function no longer appears to handle the commutativity of the expression, despite using the doCommute option. E.g. $2*(17x+2)$ is not acccepted, however $(17x+2)*2$ is.

#### Chris Graham1 year, 11 months ago

Saved a checkpoint:

Checkpointing before looking at the problem with the user defined function mark_factorised which no longer appears to be functioning correctly.

#### Chris Graham1 year, 11 months ago

Gave some feedback: Has some problems

Published this.

#### Christian Lawson-Perfect3 years ago

Gave some feedback: Ready to use

#### Christian Lawson-Perfect3 years ago

Saved a checkpoint:

It works!

I've rejigged the advice - each part's advice now begins with a description of the common factors, and I've been very careful about the use of brackets so that it's obvious what "pulling outside the brackets" means.

#### Christian Lawson-Perfect3 years, 1 month ago

Saved a checkpoint:

I'm working on writing a script to check that the expression really are factorised. At the moment, it expects the common factor to just be a number, which only works for part a!

#### Christian Lawson-Perfect3 years, 1 month ago

Gave some feedback: Has some problems

#### Christian Lawson-Perfect3 years, 1 month ago

Saved a checkpoint:

Factorising by finding a common (constant) factor and factorising quadratics are very different tasks. I think the scope of this question is only the first kind.

For example, to factorise $2x + 4y + 16xy$, I only need to see that $2$, $4$ and $16$ have a factor of $2$ in common. To factorise $x^2-1$, I need to know a fact about quadratics: the terms $x^2$ and $1$ don't have a proper factor in common.

So, I'm going to split the qudratics part into a separate question, leaving only the expressions with common factors.

#### Bradley Bush3 years, 1 month ago

Gave some feedback: Needs to be tested

#### Bradley Bush3 years, 1 month ago

Thank you for the advice Lauren. I have made all the changes you've suggested, I hope you don't end up having to give feedback on this one for a third time.

#### Lauren Richards3 years, 1 month ago

Gave some feedback: Has some problems

#### Lauren Richards3 years, 1 month ago

• I think it is good to give directions on making sure numbas accepts the answer, but you don't need I.E. inside the brackets, the asterisk would be fine.
• You don't need the words "there is" in the last sentence of the first section of the advice.
• Slight mistake in part ii) of the advice - it says 613 instead of 6x13 in the second bracket, before y^2.
• There isn't very much consistency in when you use X and when you use * and it gets a little confusing. Also for instance, in part a) when you state the question again before completing in in the advice, the statement of the question doesn't actually match the question in the parts, form-wise. I think you should only use * at the end, to show which form numbas would have accepted it in.
• Slight mistakes in parts iv) and v) of the advice. The second term in each stated (52) instead of (5x2) and (62) instead of (6x2). The third term in v) also stated (619) instead of (6x19).
• Typo right at the end of the advice talking about the video - bellow instead of below.
• Good question.

#### Bradley Bush3 years, 1 month ago

Gave some feedback: Needs to be tested

#### Bradley Bush3 years, 1 month ago

Thank you for the feedback, I should have fixed the marking now and improed the advice. The brackets do make everyhing look clearer. I have also included all the *'s especially seeing as they're needed for the question to be marked right now.

I havent put full stops at the end of EVERY calculation because it just feel unnecissary where they aren't part of a statement.

#### Elliott Fletcher3 years, 1 month ago

Main Parts

a) i) good

ii) There is an issue with the marking here, i had 102y+12y^2, and had the answer as 6*y*(17+2*y) which was marked incorrect and the displayed answer was 6*y(2y+17).

iii) Again there is an issue with the marking here.

In the question you don't write an * between each of the algebraic variables in the first term, making it look different to the other term. I think this then creates an issue in the marking as the displayed answer i got was xyz(41xyz+3) so the answer is only correct if you don't include the * between the variables even though in the statement you tell the students to include the * in their answer.

iv) good

v) again there is an issue with the marking here in the same way as in iii)

b)

iii) there is an issue with the marking here too, even inputting the displayed answer is marked incorrect as numbas thinks it is not a valid mathematical expression.

Advice

a) (all questions) i would write any products in brackets just for neatness, e.g 74x+62 = (2*37x)+(2*31).

Also, be careful when writing out big products of variables like xyz, i think you need to have an * between each variable

And i think there should be full stops at the end of each calculation.

b)

I think the formula for the quadratic equation should be ax^2+bx+c = (x+n1)(x+n2)

iii) i would put brackets around the products here.

Sorry for all the feedback!

#### Elliott Fletcher3 years, 1 month ago

Gave some feedback: Has some problems

#### Bradley Bush3 years, 1 month ago

Gave some feedback: Needs to be tested

#### Bradley Bush3 years, 1 month ago

Gave some feedback: Doesn't work

#### Bradley Bush3 years, 1 month ago

Thank you for your feedback, I have made all of your suggested changes apart from the a*b problem which is proving dificult to solve.

#### Lauren Richards3 years, 1 month ago

Gave some feedback: Has some problems

#### Lauren Richards3 years, 1 month ago

• You're missing the word factors in the first sentence of the statement.
• It really does not like formatting like at all. My answers to part a) were marked wrong on 3 occasions because of underuse of * in between each term which wasn't required. For part b)iii), the question was to factorise 9x^2+6x. I had written "3x(3x+2)" and then "3x*(3x+2)", both of which it said was incorrect. It wanted "3*x(3x+2)". I don't think the user will immediately jump to writing "ax*(bx+c)" or "a*x(bx+c)" so if you want them to answer the question in this format, you should state so in the question. Otherwise, it can be quite demoralising when it is just marked wrong but what they have written is technically right.
• In part a) I literally can't get it to accept my answers for love nor money. They always seem to be in the wrong form. This is either due to * not being used or the brackets being in the wrong order, for example: for the question "37xyz+31x^2y^2z^2", I wrote "x*y*z(37+31x*y*z)" which it marked as incorrect, as it wanted "x*y*z(31*x*y*z+37)". I think most students would give up and would not expel too much energy trying to get it to accept their answer in the right form. Give some guidance on the right form that it will accept or make it accept a simplified form.
• Part a)i) gave me an incorrect expected answer. The question was to factorise: "86x+62" which I wrote as "2(43x+31)" but the expected answer was "2(43x+3)" which is wrong. It had the correct answer in the advice.
• In your advice for part b), you need a space after b and your semi-colon should have a space after it before both and not before it.
• In part b)i), "the only numbers fitting this description..." should be a new sentence and capitalised. The final answer should be centred. This point also applies to part b)iv), b)v) and b)vi).
• The advice for part b)ii) seems quite short. You might want to explain what the difference of two squares is and what happens to the x terms.
• Prof should have a full stop after it.

#### Bradley Bush3 years, 1 month ago

I have made tha change now and the question is working but I was actually looking for a way to have a and b as a random vector of primes with b=(reapeat(random([1,2,3,5,7,11,13...] except a[i])),(Is there a way to code for this?). I instead ended up manually creating lists for a and b where every other prime was in a and the others were in b. Is there a way to code for this? Thank you!

#### Christian Lawson-Perfect3 years, 1 month ago

When b is a list, random(something except [b]) will exclude the list containing the list b, not each element of b. So the square brackets are wrong - you want random(something except b).

#### Bradley Bush3 years, 1 month ago

Could not get the except function to work because of the variables being vector so  have altered the vectors so the numbers they select their elements from are mutually exclusive.

#### Bradley Bush3 years, 1 month ago

Gave some feedback: Needs to be tested

#### Bradley Bush3 years, 1 month ago

Gave some feedback: Doesn't work

#### Vicky Hall3 years, 1 month ago

Question bii) asked me to factorise $x^2+4$ and the solution came up as $(x+2)(x-2)$. This needs to be fixed so that either the answer is 'has no real solutions and cannot be factorised' or the expression is $x^2-4$ instead.

Also, I would reword the question for b). There's no need for the student to complete the square for any of the expressions so I would just change it to say 'factorise the following expressions'.

#### Bradley Bush3 years, 1 month ago

I've improved on the typos and changed the lettering for the questions and the advice as well as moving and prefacing the video. I have put the viedo on the Trello list of reasources to be made and changed the x and y variables in the last question to c and d. Thank you for the feedback!

#### Bradley Bush3 years, 1 month ago

Gave some feedback: Needs to be tested

#### Chris Graham3 years, 1 month ago

Gave some feedback: Has some problems

#### Chris Graham3 years, 1 month ago

In the statement, "common factors that go into", you really mean "common factors of". You could start by stating what a factor is, if this is not covered elsewhere, e.g. what the the factors are of, say, 12.

It would be consistent with the other numbering styles to use a parenthesis after i),ii) and also place these in italics for emphasis.

In a) iv) you move away from $x,y,z$, which is a good idea: you could do a bit more of this with the other expressions.

Typo "epressions" in part (a).

"when there are no further factorisation can be done" needs re-wording.

In the advice, the same adjustment to the numbering as above. If an equation is on its own line then use display style.

In the advice for (b), the video needs some context "In the following video...", and I would probably put it at the end of this part as students are likely going to be more interested in the specific solution in the first instance. A very valid alternative would be to add this as a step to part (b).

I think it would be nice to have a video for both parts, and if one does not exist for part (a) then you could create two new ones (or add to the list to be created).

#### Bradley Bush3 years, 1 month ago

I am not sure whether I am being pedantic but I am unhappy with the spacing of the equations and the video in the advice section.

#### Bradley Bush3 years, 1 month ago

Gave some feedback: Needs to be tested

#### Bradley Bush3 years, 1 month ago

Created this.
Name Status Author Last Modified
Extract common factors of polynomials Has some problems Bradley Bush 20/11/2019 14:38
Factorise various quadratics Should not be used Christian Lawson-Perfect 20/11/2019 14:38
Marlon's copy of Extract common factors of polynomials draft Marlon Arcila 03/02/2018 16:28
Factor polynomials by extracting greatest common factor draft Joseph Mastromatteo 29/03/2018 15:44
Joël's copy of Extract common factors of polynomials draft Joël Cohen 27/08/2018 12:27
J. Richard's copy of Extract common factors of polynomials draft J. Richard Snape 26/09/2018 13:55
J. Richard's copy of Extract common factors of polynomials draft J. Richard Snape 03/10/2019 10:26
Extract common factors of polynomials - bugfix draft J. Richard Snape 03/10/2019 15:27
Dulce's copy of Extract common factors of polynomials Ready to use Dulce Sanchez - Macalino 14/05/2020 11:36

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