VCE Methods Question Thread!

[plato]

Thanks so much guys 

plato since you use the classpad could you help me with this issue?

How come when i antidifferentiate by hand i get

but when i  antidifferentiate using the CAS i get  ?

I am using the casio classpad 400.

Does you know whats wrong with my CAS?

Thanks 

I thought I had answered this earlier. Anyway, I suspect you have the value of -9/8 allocated to a variable "c" . You can check this by going to the variable keyboard and choosing "c" and hit EXE. Whether or not this shows -9/8, I suggest you clear all variables and then try the integration by CAS again.

[plato]

could ii please get an answer to this questions?
i got k = +/- root(-4m), for m<0 but im not sure if im right

I agree with your answer.
mx=x³-kx²
x³-kx²-mx=0
x=0 or x²-kx-m=0
There is one solution for x=0 and we want one more from the quadratic.
If the quadratic is to have one solution, then b²-4ac=0
ie  (-k)²-4(1)(-m)=0
and hence k=+/-root(-4m)

[knightrider]

I thought I had answered this earlier. Anyway, I suspect you have the value of -9/8 allocated to a variable "c" . You can check this by going to the variable keyboard and choosing "c" and hit EXE. Whether or not this shows -9/8, I suggest you clear all variables and then try the integration by CAS again.

Still doesnt work 

even my teachers couldn't fix it 

[Hutchoo]

Still doesnt work 

even my teachers couldn't fix it 

Factory reset your classpad

[knightrider]

Factory reset your classpad

How do you do that?

[knightrider]

How would you do this question attached ?

[plato]

How would you do this question attached ?

Use a pencil to press the small button marked RESTART on the back of the unit.

[qwerty101]

Same position as nightrider, but also a) LOL!

[plato]

Same position as nightrider, but also a) LOL!

Let's do the simpler one (Q7) here and knightrider and qwerty101 can both try the other one yourselves.
Start with   

Substitute a dummy variable, u
If we let u=3x then    and

Also, when x = 0, u = 3x = 0
and when x = 3, u = 3x = 9

Now, by substitution
 





But we are given
Then is also equal to 5 since u is just a dummy variable.
Hence




=

[knightrider]

Let's do the simpler one (Q7) here and knightrider and qwerty101 can both try the other one yourselves.
Start with   

If we let u=3x then    and

Also, when x = 0, u = 3x = 0
and when x = 3, u = 3x = 9

Now, by substitution
 





But we are given
Therefore is also equal to 5
Hence




=

Thanks plato 

but i don't get  this step

Now, by substitution
 

(how is it u=1 isnt it meant to be u=0)

[keltingmeith]

Thanks plato 

but i don't get  this step

Now, by substitution
 

(how is it u=1 isnt it meant to be u=0)

From what I can see, that's a typo. Check earlier in plato's post.

[plato]

My bad.
Typo now fixed.

[knightrider]

Would we ever get questions like the above on an exam ?

[plato]

Would we ever get questions like the above on an exam ?

I really don't know but I suspect it is a little too complex for a Methods exam but maybe more applicable to Specialist exams. Even then I would tend to think that a "u" substitution would involve an indefinite integral only.

[keltingmeith]

I really don't know but I suspect it is a little too complex for a Methods exam but maybe more applicable to Specialist exams. Even then I would tend to think that a "u" substitution would involve an indefinite integral only.

U-substitutions of definite integrals come up every year in the spec exams, don't know what you're talking about?

As for methods, I wouldn't expect this question to come up at all on a VCAA paper.