Technology Syntax?

[Brytz]

Hello. I've been reading Assessment reports in preparation for the Methods exams for the next couple exams. One of the reoccurring statement in these reports is the avoidance of technology syntax. (Using a TI-nSpire CAS OS3.2)

Now my teacher said that if I put solve(2x=cos(x),x)|0<x<4 on an entry line, this is sufficient working out. But I don't want to lose marks for writing this on an entry line.

Another example is probability, I write Pr(X>2)=binomCdf(4,0.5,3,4)=0.3125

Is this sufficient or do I have to write something else to gain the marks?

[CossieG]

You can't use calculator syntax. what you wrote, specifically binomcdf etc etc is not allowed. Personally, for questions involving binomial distributions I just write "this is a binomial distribution with n=x and p=a" etc etc, but you could just write Bi(a,b).

[Stevensmay]

I would write the solve one out in a nicer way.
Solve 2x=cos(x) for x given that 0<x<4
Depending on marks this may require manipulation to gain them.

Writing binomCdf will not get you a mark.
You need to show actual maths, this could be drawing a diagram, z-score conversion, making note of symmetry and others.
Also stating the type of distribution can net a mark sometimes ~ with correct values.

[achre]

Even less for both. For the algebra, I just write out the equation - 2x=cos(x) - and then I write an arrow from that to w/e 'x' equals (equivalently, you could just write "from the CAS, x=..."). For prob, you just write X~binom (n=4, p=0.5), Pr (X > 2)=whatever. The difference is that binom(n=4, p=0.5) is convention and binomcdf(4, 0.5, 3, 4) is syntax.

[Damoz.G]

I was wondering where my Post went. The OP made two threads.

Reposting....

Both of those things you put up are CAS Syntax, and if a question is worth more than a mark, you would lose the mark for working out.

For the first one, just say: "let cos(x)=2x and solve for x". As cheesy as it sounds, make it sound more conversational and communicate with your assessor.

For the second one, just say: "Bi (n=4, p=0.5)" and then write write lower and upper bound and their figures after it. Thats what another teacher at my school said to do, but my teacher said if you write each bit out, then its fine. e.g. "n=4, p=0.5, lower bound=3, upper bound=4"

Hope this helps!

[Brytz]

I posted in the wrong board by accident. And thought the Methods board would be more active.

So for solve in general, if I write something like solve for x and y for y=cos2x and y=2 where 0<x<1. Is that a better way of writing it.

Also for probability, should I write something like X~Bi(8,0.5),Pr(X>5)=0.1445

And for normal distributions Pr(X<106)=Pr(Z<2)

N~(100,3) for a normal distribution.

[achre]

I posted in the wrong board by accident. And thought the Methods board would be more active.

So for solve in general, if I write something like solve for x and y for y=cos2x and y=2 where 0<x<1. Is that a better way of writing it.

Also for probability, should I write something like X~Bi(8,0.5),Pr(X>5)=0.1445

And for normal distributions Pr(X<106)=Pr(Z<2)

N~(100,3) for a normal distribution.

It's important to specify what 8 and 0.5 are, or what 100 and 3 are. n, p for bi and mu, sigma^2 for normal.

[Brytz]

Do you have to write the variance instead of the standard deviation for a normal distribution?

So X~Bi(n=3,p=0.5),Pr(X>1)=0.5 is sufficient?

[achre]

Yes and yes.
Well, 90% sure it's sigma^2, 100% sure your binom notation will be fine every time.

[Brytz]

Thanks, can't believe my teacher hasn't told me this earlier in the year and I find out two days before the CAS exam.

Is this sufficient for the solve based fuctionality?
solve for x and y for y=cos2x and y=2 where 0<x<1

[Brytz]

One more question, for maximum and minimum problems, I often use this notation on the calculator. How would I write something like this on the exam paper to avoid calculator syntax?

[Stevensmay]

If it's not obvious from the graph, differentiate the function, let it =0 and solve for x.

[Lucho23]

One more question, for maximum and minimum problems, I often use this notation on the calculator. How would I write something like this on the exam paper to avoid calculator syntax?

(Image removed from quote.)

I guess it depends on the marks.

If its two marks for a maximum and a minimum, a simple stating of the maximum and minimum should be sufficient.
If its greater than two marks, possibly a derivative function equal to 0 and solving may be required.
If the restrictions, so the x minimums and maximums, include the f(x) maximum and minimum, I think stating would be fine. Maybe, for safety, sub the x values into f(x) and show that the maximum and minimum are at these endpoints.

[Brytz]

Okay then, just the main thing is sometimes when you solve the derivative for zero, you get both the maximum and the minimum so it takes more time to verify it is a maximum or minimum then doing it the way mentioned above. Thanks for you help.

[Lucho23]

Okay then, just the main thing is sometimes when you solve the derivative for zero, you get both the maximum and the minimum so it takes more time to verify it is a maximum or minimum then doing it the way mentioned above. Thanks for you help.

You're right, that makes sense. You may want to indicate when the derivative function/original function is greater than 0 or less than 0 approaching a maximum/minimum.
So when you have say a cubic function that has a local maximum at (-2,4) and a local minimum at (3,-2), you can say, for example:
f'(x)>0 for x<-2, f'(x)=0 for x=-2 and f'(x)<0 for -2<x<3, therefore (-2,4) is a local maximum.

Hope this helps