Higher Level Circle/Line

johnmcdnl

Am I allowed to use constructions to find the answers to these 2 questions... eg given 3 points on a circle find the centre of the circle or something like that....

am i allowed to draw the given circle and use methods i've learned in tg and drawing to figure our the centre of the circle.. eg here i'd just bisect the 2 lines formed and the pt of intersection would be the centre...

i know how to do the written part but i'm very prone to silly errors so...

but is it acceptable to get the answers by constructions.. i know that i'll not get any attempt marks but if it's right it's right.. full marks????

anyone able to help

**Timbuk2**

I really don't think so. It's not what the emphasis is about in those questions. If it didn't take long, you could always do it to check your answer

johnmcdnl

like the sketch or whatever takes me about a minute to do.. and i have every intention of doing the numbers afterwards.. but in the likely event of me making a sign error somewhere along the line it'd be nice to have the backup that i did get the right answer but using an alternative method... with the written bit showing that i understood how to do the maths behind it...

saying that i could get lucky and have it work out for me but in case it doesn't...

Afaik I remember seeing in the marking schemes that they don't award marks for drawing it. You should check it out but I really don't think so, it is, after all, a maths exam, not a tech graph exam.

wonderfulname

johnmcdnl wrote: »

Am I allowed to use constructions to find the answers to these 2 questions... eg given 3 points on a circle find the centre of the circle or something like that....

am i allowed to draw the given circle and use methods i've learned in tg and drawing to figure our the centre of the circle.. eg here i'd just bisect the 2 lines formed and the pt of intersection would be the centre...

i know how to do the written part but i'm very prone to silly errors so...

but is it acceptable to get the answers by constructions.. i know that i'll not get any attempt marks but if it's right it's right.. full marks????

anyone able to help

Short answer, no. Your being tested on the method but you can use constructions to satisfy yourself that any strange looking answers are correct I do it all the time.

zoom!

no, ur being tested on your mathematical ability not your ability to draw.

wonderfulname

zoom! wrote: »

no, ur being tested on your mathematical ability not your ability to draw.

The methods he is suggesting actually are geometric, in fact some basic ones appear on the Junior cert paper. They're just not the methods on the curriculum for Leaving cert.

johnmcdnl

wonderfulname wrote: »

The methods he is suggesting actually are geometric, in fact some basic ones appear on the Junior cert paper. They're just not the methods on the curriculum for Leaving cert.

yeah geometric basically... like i'm bisecting a line as i know that the perpendicular bisector passes through the centre... therefore the pt of intersection would be the centre...

i'd probably just do the sum out this way but it's just that i know i'm going to mess a sign up somewhere.... but by showing the correct mathematical methods and getting a correct answer.... together should i not get the marks for being right..

johnmcdnl

10. Particular cases, verifications and answers derived from diagrams (unless requested) qualify
for attempt marks at most.

found that on a marking scheme there... awh well.. suppose i'll have to stick with the maths and hope no sign errors...

suppose thread can be closed now

ajjmk

i got marks for that in my jc i think,,! but i dont think its acceptable for lc....pity, cos id be savage at those qs then! :cool:

MathsManiac

Having said all that, it's useful to be able to do it geometrically, because then you can mimic that process algebraically.

In this case, once you understand that you can find the centre of a circle by drawing the perpendicular bisectors of the chords, you can then instead find the equations of those bisectors and solve them simultaneously.

(Also, an accurate diagram can give you peace of mind by confirming your answer, and help you track down a mistake if there is one.)

johnmcdnl

MathsManiac wrote: »

Having said all that, it's useful to be able to do it geometrically, because then you can mimic that process algebraically.

In this case, once you understand that you can find the centre of a circle by drawing the perpendicular bisectors of the chords, you can then instead find the equations of those bisectors and solve them simultaneously.

(Also, an accurate diagram can give you peace of mind by confirming your answer, and help you track down a mistake if there is one.)

that's the way i'd nearly automatically do and the nice acurate diagram can show me what i'm aiming to get so i can see from a mile off if i'm going wrong somewhere... etc etc... just a pity I can't just take the answer straight but at least I know now is all

zam

Maybe draw it out to get the answer and then write it out mathematically. At least then you know the answer you're looking for