Vectors-Please Help me out

If a and b are two vectors then the value of (a+b)x(a-b) is
(a)2(bxa) (b)-2(bxa)
(c)bxa (d)axb

17 Answers

7
Sigma ·

@ Arnab: Anik doesn't live in Kolkata, i guess... How can he go to Supriyo Sir???

158
Anik Chatterjee ·

ya @subhomoy ...got it...the right hand thumb rule (or right hand screw rule)

49
Subhomoy Bakshi ·

Yeah. AGES it is.
I did not recognise you, though. :|

7
Sigma ·

@Subhomoy: Nice to see you here after AGES perhaps..

49
Subhomoy Bakshi ·

lol. why is "Suprio Sir" hidden in all the posts?

Answering the doubt:

axb and bxa have the same magnitude i.e. absinθ but they are opposite in direction (do you know the right hand thumb rule?)

thus, axb= - bxa

21
Shubhodip ·

ROFL at Arnab

158
Anik Chatterjee ·

@Sigmaya ur correct...i m frm mumbai

7
Sigma ·

no. Some of my Friends go. Do U?

21
Arnab Kundu ·

@ Sigma Do you?

11
Sambit Senapati ·

Taking a=axi+ayj+azk and b=bxi+byj+bzk
We get the answer as (a).
If anyone has a shorter method please post it.

158
Anik Chatterjee ·

no sorry...arnab...i dont know Suprio Sir...

158
Anik Chatterjee ·

ya aditya...but...why is axb=-bxa...??

262
Aditya Bhutra ·

(\vec{a}+\vec{b})\text{x}(\vec{a}-\vec{b}) = \vec{a}\text{x}\vec{a} - \vec{a}\text{x}\vec{b} + \vec{b}\text{x}\vec{a} -\vec{b}\text{x}\vec{b}

now we know , \vec{a}\text{x}\vec{a} = 0 \mid \vec{a}\text{x}\vec{b} = - \vec{b}\text{x}\vec{a}

(\vec{a}+\vec{b})\text{x}(\vec{a}-\vec{b}) = 2\vec{b}\text{x}\vec{a}

21
Arnab Kundu ·

er- Sorry for talking off the topic...
I am posting it in here cz i know i wont get the answer within a month if i post it in your chatbox....

But by any chance do you study under Suprio Sir... Anik?

158
Anik Chatterjee ·

can u show how should we do it....aditya

262
Aditya Bhutra ·

why not do direct multiplication ?

158
Anik Chatterjee ·

ya .....option (a) is correct

Your Answer

Close [X]