Comments on: Till Death Do Us Part http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part Sassy O Level Maths Tuition, Questions & Tips from Singapore's Favourite Private Tutor Sun, 05 Feb 2012 17:08:39 +0000 hourly 1 By: Miss Loi http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12494 Miss Loi Wed, 27 Aug 2008 06:31:55 +0000 http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12494 <b>.I:</b> Perhaps. That's why it's always important to note the <em>order</em> of the letters in vectors e.g. <m>vec{AB} = -vec{BA}</m> Speaking of which, Li-sa seems to have disappeared after leaving that mysterious truncated comment. Could she have been trapped in a <a href="/questions/a-maths/the-infinite-steps-to-salvation" rel="nofollow">recurrent time warp</a> like what happened to Miss Loi awhile ago? .I: Perhaps. That's why it's always important to note the order of the letters in vectors e.g. vec{AB} = -vec{BA}

Speaking of which, Li-sa seems to have disappeared after leaving that mysterious truncated comment. Could she have been trapped in a recurrent time warp like what happened to Miss Loi awhile ago?

]]> By: .l http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12360 .l Mon, 25 Aug 2008 12:24:30 +0000 http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12360 Maybe "Li-sa" got k = -1 because she had somehow forgotten the question. Instead of subtracting [pmath]vec{OP}[/pmath] by [pmath]vec{OR}[/pmath] she added [pmath]vec{OR}[/pmath] to [pmath]vec{RP}[/pmath]. Maybe "Li-sa" got k = -1 because she had somehow forgotten the question. Instead of subtracting vec{OP} by vec{OR} she added vec{OR} to vec{RP}.

]]> By: Miss Loi http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12342 Miss Loi Mon, 25 Aug 2008 06:01:08 +0000 http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12342 <b>Cendrine:</b> Thanks for your feedback :) *Scraps title of next blog post: "Welcome To Hell"* Cendrine: Thanks for your feedback :)

*Scraps title of next blog post: "Welcome To Hell"*

]]> By: cendrine http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12290 cendrine Sun, 24 Aug 2008 17:21:46 +0000 http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12290 erm....why such a title ? Dun sound good lei in this month... :) erm....why such a title ? Dun sound good lei in this month... :)

]]> By: Miss Loi http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12119 Miss Loi Fri, 22 Aug 2008 16:44:59 +0000 http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12119 <b>Li-sa</b>, umm ... your comment got truncated? Li-sa, umm ... your comment got truncated?

]]> By: Li-sa http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12109 Li-sa Fri, 22 Aug 2008 13:23:24 +0000 http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12109 Good thing you pointed that out. It implies that Good thing you pointed that out. It implies that

]]> By: Miss Loi http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12045 Miss Loi Thu, 21 Aug 2008 17:00:09 +0000 http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12045 <span class="big">如 ... 来 ... 神 ... 掌!!!</span> (in the <em>direction</em> of <m>vec{QR}</m>) *PIAAAAAAK* 如 ... 来 ... 神 ... 掌!!! (in the direction of vec{QR})

*PIAAAAAAK*

]]> By: Li-sa http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12023 Li-sa Thu, 21 Aug 2008 10:42:17 +0000 http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-12023 <span class="highlight">Usually when you see vector questions involving a <em>grid</em> like this one, expect to do some 'shifting'/'lengthening' of the vectors to form a couple of triangles (as shown in the ADDITION/SUBTRACTION OF VECTORS section of the notes above)</span> 1. 3a-4b <div class="highlight"> <img src="http://www.exampaper.com.sg/blog/wp-content/uploads/2008/08/vector-grid-answer-1.gif" alt="Vector grid answer 1" /> Pretty straightforward to form the triangle consisting of 3 units of vector <var class="vector">a</var> and 4 units of <var class="vector">b</var>. Looking at the direction of the arrows, you can see that 3<var class="vector">a</var> = <m>vec{OP}</m> + 4<var class="vector">b</var> ⇒ <m>vec{OP}</m> = 3<var class="vector">a</var> - 4<var class="vector">b</var> </div> 2. Q:(F,3) <div class="highlight"> <img src="http://www.exampaper.com.sg/blog/wp-content/uploads/2008/08/vector-grid-answer-2.gif" alt="Vector grid answer 2" /> Shifting <var class="vector">a</var> and <var class="vector">b</var> to form a triangle with a point at <var>O</var> (since we're finding <m>vec{OQ}</m> so one end <em>has</em> to be at <var>O</var>) we can then locate <var>Q</var> to be a (F, 3). </div> 3i. R:(D,3) ii. h=3, k=-1 <div class="highlight"> <img src="http://www.exampaper.com.sg/blog/wp-content/uploads/2008/08/vector-grid-answer-3.gif" alt="Vector grid answer 3" /> Now, <m>vec{OR} = h vec{OQ}</m> which means that <m>vec{OR}</m> is parallel to <m>vec{OQ}</m> (from the Scalar Multiple portion of the notes above). Furthermore, since there's a common point <var>O</var> this means that <var>R</var> must lie somewhere along grid-line #3. <m>vec{PR}</m> = <var>k</var><var class="vector">b</var> means that <m>vec{PR}</m> has to be parallel to <var class="vector">b</var>. And with the vector originating from point <var>P</var>, this means that <var>R</var> must lie somewhere along grid-line #D. So from this info, we can locate <var>R</var> at (D, 3) in the grid. And looking at the diagram, <m>vec{OR}</m> is three times longer than <m>vec{OQ}</m> and in the same direction ⇒ <var>h</var> = 3 <m>vec{PR}</m> is the same length as <var class="vector">b</var> and in the same direction ⇒ <var>k</var> = 1 <strong>Care to share how you got <var>k</var> = -1 in your answer when <m>vec{PR}</m> is in the SAME DIRECTION as <var class="vector">b</var>???</strong> *scratch head* </div> Usually when you see vector questions involving a grid like this one, expect to do some 'shifting'/'lengthening' of the vectors to form a couple of triangles (as shown in the ADDITION/SUBTRACTION OF VECTORS section of the notes above)

1. 3a-4b

Vector grid answer 1

Pretty straightforward to form the triangle consisting of 3 units of vector a and 4 units of b. Looking at the direction of the arrows, you can see that

3a = vec{OP} + 4b
⇒ vec{OP} = 3a - 4b

2. Q:(F,3)

Vector grid answer 2

Shifting a and b to form a triangle with a point at O (since we're finding vec{OQ} so one end has to be at O) we can then locate Q to be a (F, 3).

3i. R:(D,3)
ii. h=3, k=-1

Vector grid answer 3

Now, vec{OR} = h vec{OQ} which means that vec{OR} is parallel to vec{OQ} (from the Scalar Multiple portion of the notes above). Furthermore, since there's a common point O this means that R must lie somewhere along grid-line #3.

vec{PR} = kb means that vec{PR} has to be parallel to b. And with the vector originating from point P, this means that R must lie somewhere along grid-line #D.

So from this info, we can locate R at (D, 3) in the grid.

And looking at the diagram,

vec{OR} is three times longer than vec{OQ} and in the same direction ⇒ h = 3
vec{PR} is the same length as b and in the same direction ⇒ k = 1

Care to share how you got k = -1 in your answer when vec{PR} is in the SAME DIRECTION as b??? *scratch head*

]]> By: Miss Loi http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-36945 Miss Loi Tue, 19 Aug 2008 21:36:43 +0000 http://www.exampaper.com.sg/questions/e-maths/till-death-do-us-part#comment-36945 <span class="topsy_trackback_comment"><span class="topsy_twitter_username"><span class="topsy_trackback_content">Please help Miss Loi kill the fly ( http://tinyurl.com/5nfqkt)</span></span> Please help Miss Loi kill the fly ( http://tinyurl.com/5nfqkt)

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