FTSE questions.........

Q1. A fixed Pt. P(5,2) is given and two points A and B on x=y and y=0,
Find:
i) coordinates of A for |PA+PB+PC|min
ii) coordinates of B for |PA+PB+PC|min
iii) value of |PA+PB+PC|min

33 Answers

62
Lokesh Verma ·

yup this is correct..

and the solution is very simple u can make use of it!

33
Abhishek Priyam ·

Q.2 Q.3 i solved in exam, Q.1 became too lengthy does a shortcut there Q.4 nahi bana....

33
Abhishek Priyam ·

Q.5 (need hint)
ay-by=logxb (given)

then find the area of rectangle..... in fig.....

33
Abhishek Priyam ·

1
Kumar Saurabh ·

i dont understand the question!

33
Abhishek Priyam ·

U have 2 find the area of the rectangle formed by y axis and three lines such that two vertices are on given graph

1
Kumar Saurabh ·

my answer i get is

x(logax-logbx)

how it constant for all x?

33
Abhishek Priyam ·

also,
ay-by=logxb (given)

33
Abhishek Priyam ·

i think it should be such that light travels as shown after reflections....

any comments??

62
Lokesh Verma ·

hey priyam any success on these?

The last one seems to be a bit tricky.. i guess i will have to give it some time..

din click on the first look :)

62
Lokesh Verma ·

if u dont figure out.. do let me know. it is very easy..

btw when i post the solution of

http://targetiit.com/iit_jee_forum/posts/10th_november_2008_480.html

It will become crystal clear to u..

Right now u might be using similar triangles and crap.. then u might not need anything other than a straight line!!

:)

1
E=mc^2 darkangel ·

is the answer (29/7,29/7) on x=y
and (29/10,0) on x axis

i took the image point q of p taking x axis as mirror then took q's image r taking x=y as mirror then joined r and p which is a straight line and also the minimum distance as we know that minimum distance b/w two points is a straight line

62
Lokesh Verma ·

I remember /7 in the denominator when i solved..

ur method is perfect..
I cant say the final answer cos i will nedd to check..

just tell the 2 points that u joined.. then we will be sure that u are absovlutely correct :)

good work coolspirit :)

gr8 that u got the method i was talking :)

1
E=mc^2 darkangel ·

is the answer of 3rd one 1-1/10C5

62
Lokesh Verma ·

yes i got the same answer :)

1
kunalb Bhattacharya ·

Let s=(a.b'+a'.b)/|ab|---1
we know |ab|=|a||b|
we consider a=x+iy--2 & b=p+iq---3...
..On putttin 2 & 3 in 1 along with resp conjugates we get-----
s=2(px+qy)/√{(x2+y2)(p2+q2)}...thus s is real always...

Hence we proceed as under.....

s2=(a.b'+a'.b)2/|a|2|b|2
s2={(a.b'-a'.b)/|ab|}2+4{(aa')(bb')/|a|2|b|2}
........THE LAST STEP ABOVE IS IMP.....

now...we know aa'=|a|2....same 4 bb'....

thus now...
s2={(a.b'-a'.b)/|ab|}2+4

now subtracting any 2 diff complex num of the above exp can giv any real num other than 0....thus greatest value of the exp in braces is zero....

s2=4
......max(s)=2.......(Ans)

33
Abhishek Priyam ·

Thnx

33
Abhishek Priyam ·

Q2. max value of (a.b'+a'.b)/|ab| a and b are complex no and a' means a conjugate.....

33
Abhishek Priyam ·

in complex no question max is asked

1
Kumar Saurabh ·

haha. dont worry friend.

your help is very good

33
Abhishek Priyam ·

i have not tried it in test so will have 2 try....

actually paper was too fitting wala ......

1
Kumar Saurabh ·

is answer for one for equilateral trainge?

I am taking guess

33
Abhishek Priyam ·

Oh now i am totally messed up i will collect the question and post it later......... i don.t remember questions i solve and forget it....

1
Kumar Saurabh ·

ok i try both

33
Abhishek Priyam ·

Oh perhaps max was asked

62
Lokesh Verma ·

why not -ve?

1
Kumar Saurabh ·

2 answer will be 0

a=1
b=i

1
Kumar Saurabh ·

no problem friend.. atleast u give good problems.. i like ur questions.. nd learn also :)

33
Abhishek Priyam ·

a and b are complex

aur haan din bhar 7 and half hour test dene ke baad itna galti ho jata hai

that is |PA+PB+AB|min

1
Kumar Saurabh ·

in 2 what conjugate of vector?

conjugate is of complex!

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