Question

i'll use the tool
excuse me,

Answer 1

a and b are vectors,
a=(x1,y1) b=(x2,y2)
\[\left| a \right|\left| b \right|=\left| adotb \right| \]
then why x1y2-x2y1=0 ?
please help me

Answer 2

plus they are not 0 vectors

Answer 3

have you tried this ? its just algebraic manipulations....

Answer 4

if you know \( |a|= \sqrt{x_1^2+y_1^2}\)
\( |b|= \sqrt{x_2^2+y_2^2}\)
\(|a.b|=x_1x_2+y_1y_2\)

Answer 5

substitute these and square both sides, what you get ?

Answer 6

i see, since you have disappeared offline, i'll write down few steps.
\((x_1^2+y_1^2)(x_2^2+y_2^2)= (x_1x_2+y_1y_2)^2\)
Expand both sides, and you'll see \(x_1^2x_2^2+y_1^2y_2^2\) gets cancelled from both sides,
what remains will give you \((x_1y_2-x_2y_1)^2=0\) which gives you required result.

Answer 7

thank you, @hartnn
and sorry for disappearing
i was using wrong aspects, which made me go nowhere.
thanks again