21ROFL at Arnab
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
-
UP 0 DOWN 0 0 17
17 Answers
7@ Arnab: Anik doesn't live in Kolkata, i guess... How can he go to Supriyo Sir???
158ya @subhomoy ...got it...the right hand thumb rule (or right hand screw rule)
49lol. 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
11Taking a=axi+ayj+azk and b=bxi+byj+bzk
We get the answer as (a).
If anyone has a shorter method please post it.
262(\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}
21er- 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?