If 'a' and 'b' are unit vectors and |a+b| = sqrt(3)

what is (2a-5b)·(b + 3a)?

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- Oct 1st 2008, 07:25 PMzerobladexVector dot products problem
If 'a' and 'b' are unit vectors and |a+b| = sqrt(3)

what is (2a-5b)**·**(b + 3a)? - Oct 2nd 2008, 12:07 AMwisterville
Hello,

a·a=b·b=1.

(a+b)·(a+b)=3 implies a·a+2a·b+b·b=3.

Once you know a·b, substitute in (2a-5b)·(b + 3a)=2a·b+6a·a-5b·b-15a·b.

Bye.