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# Vectors – Never In An E-Maths Question

(7)
Tuition given in the topic of A-Maths Tuition Questions from the desk of at 5:00 pm (Singapore time)

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Miss Loi’s mouthful of words from yesterday’s E-Maths vector question covered, as mentioned, almost 75% of the A-Maths Vector syllabus.

The remaining 25%, then, is summarized in the following commandments:

If |u| = 1, u is known as a unit vector. The unit vector in the direction of a given vector a is a/|u|.

With the two simple statements above, unit vectors are forever cast within the exclusive domain of the A-Maths Vectors Club, thus depriving the relieved masses of E-Maths students from ever needing to waste a single brain cell on a question like this:

The vector has magnitude 85 and is in the opposite direction of . Express as a column vector. The vector is . Obtain the unit vector in the direction of .

IMPORTANT: To avert a tragedy, always double-check the order of the letters in the vectors and don’t drive in the wrong direction against the traffic!

### Revision Exercise

To show that you have understood what Miss Loi just taught you from the centre, you must:

1. kiroii commented in tuition class

2007
Jul
27
Fri
4:38pm

1

uh i dunno how to type de workings usin keyboard so i'll juz present de ans
OA = (-75)
(60)

OB = (-110)
(123 )

2. Miss Loi Friend Miss Loi on Facebook @MissLoi commented in tuition class

2007
Jul
27
Fri
11:32pm

2

Sorry Kiroii, but your answer is far from the truth!

You need to understand the concept of unit vectors well before you do this question.

Miss Loi would like to look at your workings. Check out this post on how to display mathematical symbols in comments.

Do check out the syntax guide and test out your equation first before posting here!

3. kiroii commented in tuition class

2007
Jul
28
Sat
11:29am

3

since OA is in de opposite direction of
( 8 )
(-15)
by flippin it to ( -15)
( 8 ) you 'flipped' wrongly here!
Then 1/(root square of [ (8^2) ( -15^2)]
and we'll get 1/17. Now 1/17 x (-15) x 85
( 8)
OA = (-75)
(40 )
from here OB is no biggie yes? ps: i dun see whats wrong wit my workings and sry abt de format cant seem to install the plugin ya recommanded

4. Miss Loi Friend Miss Loi on Facebook @MissLoi commented in tuition class

2007
Jul
28
Sat
10:36pm

4

kiroii, the opposite direction of is !

So
=
=
=

So can you get from here? Don't forget to express the final answer in unit vector coz that's what the question asked for. Too many students have lost valuable marks here simple coz they didn't read the question properly.

Don't anyhow 'flip' again! Know your directions well!

5. kiroii commented in tuition class

2007
Jul
28
Sat
11:40pm

5

-___-" yes mdm? truth is my sch hasnt taught vectors yet so my understanding of it is rather questionable >.>

anyway BA = OA - OB, OB = OA - BA
OB = (-75)
( 12)

6. Miss Loi Friend Miss Loi on Facebook @MissLoi commented in tuition class

2007
Jul
29
Sun
12:50pm

6

Are you currently in Sec 4? If so, quite surprising that vectors have not yet been taught at this stage.

Wei wei wei ... you're getting more and more careless!

=
= !

UNIT VECTOR in the direction of
=

What did Miss Loi just said in the previous comment?! Grrr...

7. kiroii commented in tuition class

2007
Jul
29
Sun
2:01pm

7

-___- nah priv sch oh unit vector.. i read it as column vector hahas? anyway if i may exonerate myself by sayin my understandin of vectors is rather questionable? LOL

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