Question

if u1 and u2 are orthogonal unit vectors and v = au1 +bu2, find v dot u1.

Answer 1

Use the definition of the dot product and the properties of the dot product to expand your dot product. Then, note that when two vectors are orthogonal, their dot product is equal to 0.

You should be able to get the answer from there. Let me know if you need more help.