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## Homework Statement

a) Let v be a unit vector in R^3 and u be a vector which is orthogonal to v. Show v x (v x u) = -u

b) Let v and u be orthogonal unit vectors in R^3. Show u x (v x (v x (v x u))) = -v

## Homework Equations

## The Attempt at a Solution

I am very lost in this question, I know a unit vector is = 1 therefore the summuation of the vector v is 1 for example, v = (1,0,0). square root(1^2 + 0 + 0) = 1 and i know u dot v is 0 but how do i start the prove?

thank you