Hmm... Your book and / or your instructor were supposed to have covered this material before assigning homework on it....
The "projection" of
a onto
b is defined as the vector
c that is orthogonal (perpendicular) to
b and satisfies
|b|^{2} +
|c|^{2} =
|a|^{2}.
Since
b and
c are orthogonal, what can you say about their dot product? What can you do with the magnitudes?
For explanations and the formulas to use, try reviewing a few online lessons, such as:
. . . . .Projection of One Vector Onto Another (lesson). . . . .MathWorld: Projection (article). . . . .Dot Products and Projections (lesson). . . . .The projection of a vector. . . . .Wikipedia: Vector projection. . . . .How to Project One Vector onto Another. . . . .Vectors (tutorial)Once you have learned the basic terms and techniques, please attempt the exercise. If you get stuck, you will then be able to reply with a clear listing of your steps and reasoning so far.
Thank you!