Posted by Yuni on Sunday, December 25, 2011 at 4:59am.
if a & b are perpendicular vectors, show that
a)(a+2b).(ab)=a^22b^2
b)(a+b).(ab)=a^2+b^2
*how to show it?just multiply it?if yes where doescome from?
doesshow that it should be a value?

math  drwls, Sunday, December 25, 2011 at 6:11am
  around a number means "magnitude of". You will need to use the following relationships:
a*a = a^2
b*b = b^2
a*b = 0, because they have said that a and b are perpendicular.
Th "*" operator means "dot product", which I assume you have learned the meaning of. In general, for vectors x and y,
x*y = x y cos(theta)
where theta is the angle between the two vectors. Thus, in this case,
a) (a+2b)*(ab)=
a*a a*b + 2b*a 2b*b
a^2  2b^2
Do problem (b) the same way.

math (clarification)  drwls, Sunday, December 25, 2011 at 6:29am
My first line should have read:
  around a number VECTOR means magnitude of that vector
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