Carrotsticks' 2014 Extension 1 HSC Solutions (3 Viewers)

[garfield qiu]

sorry for the inappropriate words. please forgive an esl student. some problems are from sombody else. anyway, now the solution works perfectly

 

[Samir97]

sorry for the inappropriate words. please forgive an esl student. some problems are from sombody else. anyway, now the solution works perfectly

So my solution should still be fine?

 

[emilios]

Carrotsticks, for the parametric circle q, i didnt know how to use the previous part to find the curcle equation but I could immediately see that the centre was going to be S(0,a) so I just squared the X-coordinate of Q, subtracted a from the y co-ordinate (gave me [y-a]) and i squared that, then added both squares and the final term cancelled out to just a^2. Is that considered fudging? And would I still obtain full marks?

One way of solving this q was just by doing x^2 + y^2, which you could then notice was equal to 2ay.

Your method is essentially the same. Let's hope the HSC markers aren't feeling bitchy, I think that's potential for 3/3 since the question specified you could use an 'otherwise' method.

 

[Carrotsticks]

hey carrot, would you need to show that there were 2 solutions not just one for the ski jump question to find max d? because i showed the pi/8 and justified with 2nd derivative test, but i didnt include the 2nd possible solution. will the marker take marks off for this?

arghh so I showed that there were two stat points as 22.5 degrees (pi/8) and -67.5 degrees. I showed that the 22.5 degrees was a maxima by testing points around it, but just inspection of the other one in terms of the derivative told me that it was a minima so I didn't bother proving it (I wrote that it was a stationary point though).

Carrot do you think thats okay :/

The both of you will not lose marks for this, as you did obtain the correct answer at the end of the day. You just had something extra unnecessarily.

Carrotsticks, for the parametric circle q, i didnt know how to use the previous part to find the curcle equation but I could immediately see that the centre was going to be S(0,a) so I just squared the X-coordinate of Q, subtracted a from the y co-ordinate (gave me [y-a]) and i squared that, then added both squares and the final term cancelled out to just a^2. Is that considered fudging? And would I still obtain full marks?

That is not fudging, as the result was not given to you and you were working based on intuition.

Provided all the algebraic steps are correct, you should receive full marks.

 

[Samir97]

The both of you will not lose marks for this, as you did obtain the correct answer at the end of the day. You just had something extra unnecessarily.



That is not fudging, as the result was not given to you and you were working based on intuition.

Provided all the algebraic steps are correct, you should receive full marks.

Cheers Carrotsticks! Looks like full marks are coming my way for this exam

 

[millwa]

hey carrot, sorry if you've already answered this but for parametric pt (iii) if you found QS=OS=a, is it justification enough to say Q is a variable point on fixed circle with centre S(0,a) and radius of a?

 

[Matty933]

If I get 96 external and 98 internal what would my overall be /50?

 

[youngsky]

If I get 96 external and 98 internal what would my overall be /50?

49/50

 

[Gumball]

If I get 96 external and 98 internal what would my overall be /50?

it depends because they may scale your internal down if your external is lower than internal. but ur defs looking at 48/50

 

[aDimitri]

hey carrot, sorry if you've already answered this but for parametric pt (iii) if you found QS=OS=a, is it justification enough to say Q is a variable point on fixed circle with centre S(0,a) and radius of a?

yes, this is what i did

 

[Vabz]

yes, this is what i did

Yeah, I did that as well, but will it get us full marks?
Or is it worth only 2 since the solution didn't use the gradient.
Doesn't seem enough for the full 3

 

[Carrotsticks]

It is enough for three.

 

[aDimitri]

Yeah, I did that as well, but will it get us full marks?
Or is it worth only 2 since the solution didn't use the gradient.
Doesn't seem enough for the full 3

the question said hence or otherwise
you can do literally anything within the scope of the course that is mathematically correct...